2D games will come and go always...it's not even nostalgia...it is a definite gameplay mechanic, where you don't walk freely, you walk only in 2 dimensions...thus creating a unique gameplay experience. Even if 2D dies sometime soon, if it hasn't been considered dead already for consoles, it'll come back with some good games once in a while.
Plus, 2D games usually allow for great art style, and frees up processor power for excellent 3D effects.
LEFT4DEAD411.COM
Bet with disolitude: Left4Dead will have a higher Metacritic rating than Project Origin, 3 months after the second game's release. (hasn't been 3 months but it looks like I won :-p )