I have nothing against 3D graphics. I just want the graphics to be awe-inspireing and immersive. Unfortunately, many games are much more likely to inspire a grunt, or even an uninstall, rather than awe. One of the only 3D games where I have ever felt dumstruck at the sheer beauty it all was URU. For the most part, 2D adventure games just look better.
BTW, It's a myth that people who play FPS games don't want to play 2d adventures. I play the occasional FPS, and I love adventure games. I realise you probably meant the hardcore FPS gamers, but if they don't want to play adventure games in 2D (or don't have the patience to), they probably aren't going to play 3d adventure games. Frankly, I say screw them.
It boils down to this: will the game be more immersive and look better with 3d graphics? If yes, then great. If no, then what's the point?