Lots and lots and lots of items! Random generators can be employed to increase variety. I like to be able to play over a period of weeks and still be finding new and better things to outfit my character with at the end of that period.
Random generators are great, but do you mean new and better thans as in "this sword does 30 damage when my last sword did 20", or "this sword shoots fireballs when my last sword didn't"? Do you mean better things as in just being more powerful than the last things you had, or better in that they have something that's niftier about them than the last item?
I also like a certain amount of safeness in the games I play. If permadeath is possible, there should be concrete things I can do to avoid it. If item or home loss is possible, allow me to pay a price to keep from losing them. A good portion of the fun for me in an RPG is having a character (and her items) for a long, long time.
Concrete things such as not wandering into the cave that everyone knows houses a big nasty dragon that eats experienced players for breakfast, lunch, dinner and sometimes a late night snack?

I want different things from a hack-and-slash RPG than from a roleplaying RPG, but I like and play both, so I'll outline both.
Hack-and-slash RPG:
Lots and lots and lots of items! Random generators can be employed to increase variety. I like to be able to play over a period of weeks and still be finding new and better things to outfit my character with at the end of that period.
I enjoy the standard progression whereby you kill things to get points to increase your stats so you can go to harder areas and kill harder things with better treasure. Rewards should be fairly frequent whether levels or treasure. The gameworld should also be easy to socialize in, have nice commands to chat or boot out annoying people.
Uber-realism is just a means to an end, and games can be perfectly enjoyable without it. My two main requirements are some AI to challenge me and the ability to keep upgrading and customizing my character.
Roleplaying RPG:
Some basic world and race history so I know what I'm playing is very important. Now, of course, I'm an absolute roleplaying genius and I can create fascinating characters with nothing more than a gender and an age, but nothing that lacks context is as enjoyable as it could be.
Here I also like combat, skill progression and lots of items to outfit my character (though this time, for looks as well as uberness). The rewards do not have to come as often, but I still want challenges I can meet in order to gain something, usually exp or treasure.
Things that facilitate my attachment to my character should be plenty. Looks customizations, homes, special titles I might get through roleplaying... and the ability to keep meeting challenges and earning stuff, since no matter how great the RP is, having a character that's stagnant mechanically takes some fun out of it for me.
Some snertproofing mechanics are required in roleplaying RPGs too (what a strange term I've invented).
More things I thought of after reading the rest... quests are good, even if it's as simple as the generic "fetch me [random item]" quest. It's good to have goals (another way to do this is to make sure money is never worthless, but can always buy some fantastic item or other once you have a little more).
I also like a certain amount of safeness in the games I play. If permadeath is possible, there should be concrete things I can do to avoid it. If item or home loss is possible, allow me to pay a price to keep from losing them. A good portion of the fun for me in an RPG is having a character (and her items) for a long, long time.
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