It was going to be a very interesting FPS. You had to find fuel for cars... that you had to find. You had to hunt for food. You had to sleep in 'safe' places so the mutants wouldn't harm you. Very much a RPG FPS. They've slowly been removing all of those RPG elements and it's turning into just another FPS. I'm sure it'll be interesting to play just for the environment, as the alpha/beta or whatever did look nice, but ... hm.
Oh and the actual story is that it's a fictional version of Chernobyl where mutants are everywhere and Stalkers are sent to kill stuff, iirc.