2D first-person isn't as silly as it sounds. Just look at Doom. While the graphics were presented in a manner that simulated 3D, they were actually ray-traced 2D. Ever notice that aiming straight forward shoots an enemy a floor higher, and that you are never directly underneath or above another room? If you look at the map, it's just a 2D, top-down shooter presented from a first person viewpoint.
Back to the topic at hand. It's my opinion that 2D and 3D work just about evenly. What it really comes down to is the art direction and the game design. Also, 3D games can feel a lot like their 2D ancestors, which is great in that they play like classic games, but offer another layer of depth. Sonic Adventure, Devil May Cry, and Jet Grind Radio are great examples of this.