these type of games have limited longevity

MMORPG4win.
Counterstrike=crack
I see where you're coming from, it does at first seem a bit 'same samey'. Counterstrike is, however, at least 10 different games now. (I'm not sure how you code different games into maps, but they manage to do this). So the ones I've seen so far that I like are:
Warcraft Source (Choose a class, gain XP from kills/bombs etc, spend XP to buy invisibility, lightning, teleports, damage-leeching, turning yourself into an oildrum etc).
Breakfloor: each team starts on either side of a wall, the floor consists of a large array of cubes, each of which can be broken with bullets, to allow you to tunnel into the other side.
Zombie Horde: pretty self-explanatory, run like hell, shoot the zombies, if you get bitten you join them
Gun game: the best, probably most popular, Valve are going to make it an official add-on. You don't buy anything at the start, you just head straight into the action, every time you make a kill (or 3 kills), your weapon levels up. Extremely fast-paced, brutal, no waiting around. Still plenty of strategy though. I think BlackOps has gungame too.
I've always been interested in the idea of MMORPG, I go to the big review site often, but can never find one that really suits me. Real world badness, GTA kinda style. Or a nice modern multivehicle sprawling wartime one.