QUOTE(jessenator @ Nov 11 2008, 04:40 PM)

maybe i'm old, but 2.5D seemed to me to be more of a term of endearment for the engine-style once Quake came out. So '2.5D' is offensive?

2.5D means something very specific in terms of how a game works verses how it plays. I think it has become an offensive term because a lot of people use it incorrectly and then it appears to either mean something different every time you use it or to mean simply nothing at all. It does, however, have a quite consistent and useful definition. The term itself is not flamebait, though if it is associated with people who use it incorrectly I can see how that interpretation evolved.
And now to discuss some of my favorite 2.5D games:
Wolfenstein 3D - I still get a lot of enjoyment out of this game; it is the FPS at its core, solving a level puzzle while shooting the guys that try to stop you. Plus the sound effects are timeless
Blake Stone - Very similar to Wolf3D (same engine) but a little more advanced. I've only played this a couple of times because I have to emulate the actual DOS program (i.e. graphics and controls kinda suck a lot) but it seems that a modernized port of it would be very fun indeed. Unfortunately the source code is gone so that would be a formidable task.
Doom/Doom II - What kind of FPS fan would I be if I didn't play this game? Actually this has always been one of my lesser favorite old-school shooters (I tend to get stuck in it a lot), but recently I've come to appreciate it more - the double shoutgun in Doom II is so satisfying...
Heretic - I've played through most of Heretic, and it was pretty fun but personally I like Doom more (mostly for the bigger, louder weapons).
Rise of the Triad - For some reason I always love unpopular games, and this is a perfect example. The music is awesome, there are like 5 different kinds of rocket launchers (one that actually shoots five rockets!) and when you blow up someone just the right way their endtrails (and eyeballs) come raining down the screen. It does get kind of old after a while (the gameplay changes little if at all throughout the single player) but it's still a great game... I mean, John Romero's God Mode grunts, a powerup that makes you trip on shrooms, and health pickups that are cooked enemies!? I suspect the multiplayer is really fun too, but I've never tried it.
Star Wars: Dark Forces - This game is fun enough that it is worth playing the original DOS version (of course Lucas isn't releasing the source code), but that won't matter soon because someone actually took the time and effort to effectively reverse-engineer that game's engine and modernize it. Even in its pre-beta stages the new Dark Forces is pretty damn cool. I personally cannot wait for this to get finished.
Duke Nukem 3D - For some reason the mechanics of this game work really well (for me at least)... which make it one of the best FPS games I've ever played. Plus its got that dark sense of humor that Apogee so loved. As an added bonus you get to listen to your character being a badass every time you gib an enemy or "activate" one of the many strippers throughout the game.
Well, that's all the ones I can think of, and I know what I'll probably be spending my evening doing now...