Lost Alpha is a new episode of the S.T.A.L.K.E.R. series made by dezowave group for free!
I gave a 8/10, because I'm amazed by the additional content returning to the zone from a slightly different point of view, the "fresh-old" feeling is omnipresent. It only suffers (even after newest patch) from heavy performance drain by certain features (sun lighting and view distance) and a lot of bugs and frequent crashes, which I don't have in the retail games.