Making a GAEM. COOL GAEM. It's a zombie-shootie game, with a bit more emphasis on the light heartednessnuss of life. The story as far is basically:

Nuclear powerplant explodes
Nearby cardboard factory mutates into cardboard zombies
Your parents are out of town
One boy. One watergun. One mission.

Except there's multiplayer, multiple different waterguns, and multiple missions. But alass.

I have run dry (Yeah I'm hilarious get over it) of different ideas of which to use to defend against waves of these mushy creatures, some ideas already include:

Sprinklers, which would require a constant water supply which would drain your entire water supply fairly quickly, but create an almost unpassable barrier for the enemies.

Supersoakers which fire a beam-type projectile that would soak all enemies in a line, and use a fairly large amount of water but could be refilled from your entire water supply.

Water guns, which fire a single projectile, have low weight and water costs.

Tap Trap (copyright because I'm awesome) which would require a LOT of water, but once set up create a barrier to them for a while (Think home alone, robbers stuff up the sink and let the water overflow. The enemies would slowly soak up this water.)

Water bombs, a single time low water cost that might effect a 1-5x1-5 radius depending on how much water you used (Low chance of them exploding on filling, slowly rising up to a larger chance at larger bloonz)

Bucket on the door. Classic.

I also have a few less conventional ideas, for variance;

Storm Rod summons a huge storm, instagibbing 99% of the enemies not covered, one use per game.

...okay one less conventional idea.

This is where you, the reader, come into play! I'd love to know your thoughts about this, it would be a fairly quick game, but should have a LOT of variance with which you can play around with, so a mostly unique experience most of the time. What else can I use for weapons? What other ideas do you have? Should I go with some kind of stamina system? Is health restorable through those Smarties left on the counter? This isn't my game as much as I want it to be the game for everyone else.
I like the idea. It's a unique spin on an overused premise.

I would start by focusing on core mechanics. You have already established that it will be some sort of defense game, yes? So, at it's most basic, you fend off enemies. Having health replenish only with certain items emphasizes planning and avoiding risky encounters whereas automatically regenerating health encourages more bravado. If there are rounds of play, I would lean towards health items that you can purchase between rounds. Maybe candy to restore health and band aids for use in rounds?

You may also want to consider different types of opponents to change up strategies. Examples: The basic cardboard box zombie is slow and weak but numerous. Use anti-horde strategies (area clearing items, etc.). The big cardboard monster is much tougher and stronger, but solitary, so requires much more targeted attention. Light cardboard monsters are flimsy but fast. Spawner monster is slow, weak, but tough and generates baby monsters. Tape monster doesn't hurt players, but entangles them, slowing them down.

For weapons, I like the idea that they are not just flat out weaker or stronger, but behave differently. The basic squirt pistol would probably be the starting weapon, right? Light, fairly quick, but not very strong or long range. A heavier pistol might add range or more water per shot at a decreased rate of fire. Maybe some sort of scatter shot weapon that sprays a broad area in front of the player but is very short range. Or a water balloon launcher to fling those balloons at long range (obviously would require you to fill balloons as ammo).

For traps, remember that sprinklers can spray in a variety of patterns. The basic area sprinkler, side to side sweeps, directional sprays, etc. Each would have advantages and drawbacks (for example, a directional spray covers less area, but also uses less water and is great for choke points).

Also, maybe players can build hard barriers out of boxes or something that only certain enemies can bypass (fliers) or destroy.
So far its 3 against 1.

I like it Wookie must like it to even propose it..

Jmurph - "I like the idea. It's a unique spin on an overused premise."

Who would of thought cutting fruit would become one of the largest/most popular games on the IOS platform and other platforms?
There are casual gamers on BYOND too. Just because someone plays IOS games doesn't make them a different type of gamer.
I play both mobile games and PC games. I enjoy RPGs most on both platforms.
In response to Jmurph
Thanks for the helpful reply, there's a lot of great ideas in there, and I can see you're at least mildly interested in the project! Would you mind if I got your opinion on a few ideas that spring to mind right now?

Having a finite amount of health, that starts at 100 and drops as you get attacked, like more oldschool games, as opposed to newer Jam-On-Screen-Regen style mechanics.

Only really having one or two maps, but making it/them huge, twisty, windy and varied. For example, as opposed to having three maps 'House.dmm' 'Garden.dmm' and 'Street.dmm', having a single map which initially starts at the Garden, but depending on how you're doing lets you decide to go into the house or street, a bit more like Call of Duty: Black Ops.

I would really appreciate a few more suggestions on weapons, should I go for a class-style system, where you can only hold one of SuperSoaker class and only two of WaterGun class. Or a more generic weight system with changes to the player's speed, or a hybrid system, or a more modern day shooter system of two weapons with an optional smaller side weapon.

I love the idea of having weapons which are YOURS. There are many super soakers in the world, but this one is yours. Springs to mind, and I love this whole progressive feeling of being able to keep your things and slowly upgrade them. That's in, and I don't care what people say, but how do you think I should manage this? Individual stat upgrading, such as Water Capacity and Velocity? Or larger more generic upgrades such as Tier 1 (A small increase to all stats) into Tier 2 (A larger increase) etc. Or maybe something all together more unique. Should I have weapon progressive levels? I dislike the unrealistic terms of the more you use a weapon, the better the weapon gets, but if implemented with the class based weapons above, you could level up your small arms and big arms to make a more appealing choice to you. I really don't like the idea of forcing players to use what they first started with though, and the bonuses wouldn't probably be huge.

Currency? I'm really stomped on this one. I guess it all depends on whatever the merchant ends up being, assuming I implement one. Is he some lone wolf kid, or something more? Or even better, a Dead Rising style system, where you find the parts yourself, and those in themselves are the parts. If I did this, I'd probably implement some kind of blueprint system to help out.

Water Sources. Where I live there are very few houses around, and I've rarely spent much time outside of my Island, however on my trip to Australia, I saw many neato things like Fire Hydrants and Water Tanks. What's generically available for immediate water supply around the local neighbourhood? I plan on having a hosing system you can lay down, so you can create bases around the town(?) that you can retreat to if you need to for some added defense and water.

Why do you think I made this post? I wouldn't be requesting ideas from the players if I knew already how to make it super original.

The question was never 'Hey how original is this game?', it was 'Hey how can I make this game more original and fun'.
In response to El Wookie
Large maps and small maps both have advantages and disadvantages. Larger is harder to cover for single player and small groups, but accommodates larger numbers much better. Small maps can be high pressure but get overloaded with larger numbers of mobs/players. I haven't played CoD:BO, so don't know how they deal with it.

As to classes, you always have one. The question is do you want more? Classes generally force more specialization and often have built in mechanics to encourage coop play. Even if you do not limit weapons by class, you can control how they use those weapons. So, for example, maybe the Sniper gets +2 range on all direct fire weapons (or has an advancing perk system that adds +1, +2, then +3), while the Grenadier gets an increase in blast radius. Even using the same weapons, they play different.

Weapon customization adds another step to this. I would suggest making it a system of tradeoffs. The basic components of most ranged weapons are things like range, accuracy, lethality, weight, capacity. So maybe you can put a bigger reservoir on for +capacity but also +weight or a wider bore barrel for more lethality but lower capacity (shoots more water per shot). You could augment this by having different quality parts that make the trade off more or less efficient (IE a good reservoir increases capacity by 30% with a 10% weight increase while a lower quality one has a 20% increase in both). I would probably use weight as the great equalizer, meaning the more (ad bigger) guns you carry, the less water, health restores, gadgets, etc. you can carry.

There is no reason you can't have a merchant and parts scavenging. The merchant could be a vending machine, a shifty loner, an ally that holes up during waves of enemies (see Killing Floor) or whatever. Scavenging could be based on exploration (opening cabinets, breaking crates, etc. for weapons and guns). Maybe you even sell the junk you can't use to get more money.

As to fresh water sources, in the US, there is generally a water supply provided by a utility company. Water is generally transported through large underground pipes that connect to individual properties. Properties not connected to a water supply often rely on wells, which is essentially just a tap into a below ground aquifer. Common water distribution systems include residential plumbing (faucets, toilets, showers, etc.), commercial plumbing (restrooms, drinking fountains, etc.), and emergency systems (fire hydrants, fire sprinkler systems. Home owners often set up elaborate sprinkler systems which may be manual or automatic (which can use all sorts of zone and timer systems). Commercial sprinklers tend to be automatic. Keep in mind that natural systems like rain, rivers, etc, can also provide water, but are probably not in the scope of your game. I would guess that faucets, hoses, and fountains would be used to refill (which could be hazardous while enemies are around) and that faucets could be tapped with a hose to extend the refill point to another location or to power a trap system such as sprinklers (which would prevent refills while it is hooked up). Players may also be able to carry jugs of water for portable refills at the expense of weight.

You may also want to have risks like electricity and fire to encourage creative playing. So, setting up a sprinkler near an outlet creates a risk shocking players that pass through (I would probably have it just be a stun effect that doesn't hurt the cardboard zombies) and a risk of fire from short out. While fire is bad for cardboard, it is also bad for structures and players and takes water to put out!
In response to Jmurph
Ooh I like you a lot. Completely homo. Regardless there's a lot of great information in here that I hadn't though of, using a vending machine for weapon customization is a great idea, as it gives me a realistic means of having multiple 'merchants' around the map.

The idea behind having a larger map is not to make it more difficult for single player, but instead to increase the feeling of progression throughout the game, whilst I've been trying hard to stray from comparing this to Resident Evil Online, I feel when on that game, a round is a round is a round is a round, it's just a round. I'd like something more like, the initial area is small and easy to manage, regardless of players, and slowly depending on the player's preference, unlock more areas, leading to exploration and replay value. How I could manage this to be easy in single player, I'm unsure. Maybe some kind of quick-travel across the map. But that's assuming you need to take care of the map, as opposed to just finding the most well defendable area, and holing up in it. Any ideas on how I could manage that? I guess things like powerstations (Waterstations!) are obvious candidates, but I'm sure it would still lead to the same means.

I really did think about adding fire and electricity, but ultimately decided against it. I want this to be as 'fun and cartoony' as possible, whilst keeping it realistic. I have no doubt it wouldn't be difficult to add fire and electric without making it serious, but it just wouldn't feel right, having a twelve year old character walking around with a flamethrower. FLAMMENWAFFER. IT WAFFENS FLAMMEN.

Again thanks for taking the time to help out.
In response to Complex Robot