Just finished playing both the 360 demo and PC demo. Both at 720p and on a Samsung DLP. It's the same exact demo (first level tutorial) on both platforms, and the 360 demo is very representitive of the full game, as I played it at launch. I'd give a very slight edge visually to the PC version, mostly for slightly better textures. Since I'm running at a relatively low rez (specs below), I was able to turn everything to maximum. I'm sure those with higher rez monitors will have a better time with the PC's graphics. I'm more comfortable with a joypad than a kb/m, but this isn't a game that is twitchy in nature, so it's sort of a wash anyway.
I don't think it looks as good as FEAR, nor is it as fun. Obviously just my opinion.
Athlon 64 X2 3800+
7800 GT
2 Gig Corsair XMS