On a totally random example, not of an MMO, but Fallout NV. After a couple of playthroughs I thought "hey, instead of going through the rather linear process they make the player go through in their first playthrough learning the game, how about I go the total opposite way instead".
So, I avoided the safe way, took some stealth boys, and went the really hard way. This meant I skipped the level grind in easier missions and went straight to level 10-15 territory while I'm still level 2-5.
I think the problem is that level to some degree will always be noticeable to the player and its about creating opportunities to make the game harder for oneself that helps at least myself keep interest in it.
For some other, unfortunately single player examples: certain games like Shining Force 1 and I believe Vagrant Story had progressively harder enemies on each successive gameplay. Of course this meant playing the same game multiple times before really noticing the increased difficulty (either higher enemy stats/stronger AI) but rewarded replayability.
So here is a little list of abusing the level system to make it interesting:
1) As above, instead of the player getting progressively stronger, make enemies progressively stronger. Some games already use this, The Last Remnant and others had systems where the more level grinding you did, the tougher enemies became effectively trying to stop you grinding in the first place.
2) The anti-leveling. Dragon Quarter did this by making it so every time you used a power you were closer to a game over. Admittedly this did come with a restart (a complete game restart) with certain things carrying over that made this easier, but a system which reduces your stats over time/battles promotes more careful choice of battles instead of liberal grinding.
3) The Stat leveller. Final Fantasy II had many problems with it, but one of them was also one of its better ideas at least in concept. Instead of a linear leveling system, FF II had a stat leveling system where getting hit would help increase your hp and def, attacking would help increase your att, etc. FF II could have done with some balancing on this concept but the idea was nice.
4) Equipment grind. Make classes or even no classes with a set stat level and make it so equipment, rather than experience points factor into development. This promotes greater equipment finding or purchases than combat grind.
5) Fixed modular development. Think FF X sphere grid, except when you add new spheres, you got to take some away from your current stack. This might help specialise especially in multiplayer or multi-character single player games to promote more thought into tactics. Free class changes at a touch of a button such as in FF XIII doesn't count.
6) Reset levels. Azure Dreams, one of my fav games had a level reset system each time you went into the dungeon. Of course, your monsters leveled up and never reset, and you could equipment grind to eliminate the need even to take monsters, so in a way this is more a mix of other ideas, but always starting at lv1 in an interesting concept but relies on other ideas to promote at least some sense of progression.
7) Quest based stat progression. Instead of battles, make quests lead to stat progression. This does mean making quests interesting and not-combat-centric.
8) Ensure combat is more interesting with multiple combinations. The Rock-Paper-Scissors method has been used a lot in many games, especially single player RPGs (Fire Emblem, Vandal Hearts 2, Legend of Kartia, etc) so is a bit dated. But when you have melee, ranged, magic and other features, you might be able to make it slightly more deeper. It unfortunately means however that once you learn the magic link between whats good vs what games become a drag.
These are just some ideas for making level less a number, but a journey. Ultimately though, its always there in some form or another.
Perhaps taking a leaf from other genres, and perhaps represented in Zelda titles is the concept of command-creep. I'm thinking things like Metroid as well as Zelda in this. You get things like double jump, ball morph in Metroid and bombs, boomerangs, etc in Zelda which open up new areas which you might have already tried exploring but was blocked from doing so before.
You could model your game after something like Guild Wars 1 where the leveling is very insignificant. In Guild Wars, the level cap is 20, and you can reach it inside an hour or two of play depending on which campaign you start in. After that, it's entirely dependent on the individual's skill as a player. The equipment everyone wears is rather standardized (meaning everyone has the same armor rating for their chose professions, the same weapon/weapon damage for their professions, etc). The only minute difference in gear is the enhancements like runes and insignias, but that also provides a small marginal difference.
So what I am saying is, is make it so these "levels" mean as little as possible, so players have to focus more on HOW they use their character's skills.
PS
Personally, I prefer Guild Wars 1 over it's sequel.