Hmm... it's a tough call. I happen to love Deus Ex, and the only other FPS that I like are GE, PD, and TS2. I really don't think it's like your typical FPS, for the most part. It really is an RPG, in the body of a FPS. There's a pretty good amount of time spent going around town, talking to people and whatnot. As for how the game actually plays, that largely depends on how you upgrade your guy. You can go for stealth, or a real gun-toting badass. I focused on the latter (or is it former? Gah! I always get those two mixed up), so I would have to admit that there were times where it played like a typical FPS.
I like how there's more than one way to get through an area. The best example I can think of is this one area later in the game. You start out on top of a 3 story building, and it's just crawling with guards. My guy had upgrades that allowed him to take lesser damage from high falls, so I took the rather unorthodox method up just jumping off the building. This normally would've killed my guy, but with the upgrades, I only took a moderate amount of damage. Believe me, it was much easier fighting my way IN the building, than it would've been for me to fight my way OUT.
The absolute high point of the game is where you get to Hong Kong. That's where it most feels like an RPG. You wander the streets at night with neon signs everywhere. You can visit a dance club, a Buddhist temple, or the seedy back alleys. Plus, it features a bunch of white voice actors doing horrible Chinese accents. "Oh, herro. Relcome to my estabrishment." I'm serious, they say stuff almost exactly like that. It's so bad it's good. The rest of the voice acting is pretty brilliant, however.
The game does kind of falls apart towards the end. In the final few segments of the game, it really feels more like your standard FPS. Especially the very last area, which was a bit disappointing. You pretty much just go aroung shooting stuff at the end.
I'd say that about 75% of the game is absolute gold, and the other 25% is kinda... eh. Take that as you wish.
And I liked Metroid Prime. Does that completely discredit me, Ninja?