I must admit I almost gave up on this game after my first play, as it starts quite sluggishly, your gear is initially pathetic, and mechanically you are thrown in at the deep end with little idea how to play. It also seemed to have the complexity of a role playing game yet play out generally quite linear.
BUT, after figuring it out and getting into it, it really does get good. Once you pass the initial barren areas you start entering some amazingly atmospheric set pieces like derelict laboratories, experimental sites, military complexes, and of course eventually work your way towards the reactor.
Some of the inhabitants and obstacles you come across are really quite inventive and strange too.
Well worth a play, just make sure you stick with it, it does get good!
ps. The only important tip is to keep your weight down (under 50); you cant really sprint for long otherwise and so traversing the large maps takes forever.