Rightly dubbed as the BEST. GAME. EVER.
Just the fact that you play as a scientist with almost no combat experience instead of a soldier or a gang member makes you feel all the more bad ass. This along with the fact that every archetype of video game enemy is trying to attack you (aliens, robots, zombies, and guys with guns) makes it all the more revolutionary and original. I've played through the game at least 10 times, and every play through, despite it being absolutely linear, is something to remember. I definitely recommend this game. You'd be joining one of the world's best game communities and you'd be buying a game by the world's best developers.