So, first things first. The price. about 60 euros for a game without a multilayer asset is plain too much. I'd be too much in any case, but this way it's just ridiculous.
AND it takes almost 8GB of space on your hard disk.
BUT the game's pure gold. Smooth playin', great graphic scenario, good weapon variety (you'll love shooting secondary modes), 3 difficulty levels, monsters, monsters and monsters, a flame-thrower (kids love it) a whole spaceship to destroy, a good interaction with the ambient, the most realistic game, thanks to the lack of HUD, witch emphasize the feeling of being inside a MOVE instead of a normal no-brainer game. Shading, colours, everything look like it should do. no bugs, glitch or anything. Sounds are the most thrilling thing (not like DOOM 3, but, you know.....) and there are various times in the game when it switch to something far more complicate than a first person shooter.
Get a lot of medipacs.
Note: Getting used to controls may take a bit. Don't think support joypads, at least not the PC version. The game features an 'over the shoulder' third-person perspective.