The thing I am worried about in the PC version is the control system. The game is suited perfectly toward analog sticks, both for targeting and for movement. The mouse is going to ruin that, I think.
As far as PS2... yeah, I think the graphics are gonna get hardcore fucked there, which will be a shame, because the game is absolutely beautiful. I think the optimal platform for it would be a high-end PC (see the Über-Über Box thread) with a PS2 controller (I still prefer it over everything else). If the PC version supports the use of external game pads with analog function *and* there's a PS2->PC controller adaptor... that would be how I'd want to play it.
Except that you really want it on a big ass TV to fully enjoy it.
Okay, the ideal setup for it is on a 36" Wega with 5.1 surround (man it sounds amazing) and an Xbox.