tranchemusicdanielneither
stalker shadow of chernobyl and call of pripyat if you want postapoc exploration
the witcher 2 if you want fantasy action rpg
STALKER games are good, Witcher games are kind of shit
As for the OP, I preferred Fallout. I might be biased against Skyrim though because of how terrible I think Oblivion is.
Don't forget, the company that made S.T.A.L.K.E.R. may not be planning to continue making games, but their forums are still active. Also, the S.T.A.L.K.E.R. community is pretty active too.
Oh, and don't even get me started on all the amazing mods for this game. Try searching for AMK, ZRP, S.T.A.L.K.E.R. Soup, etc. Before doing that though, always do a vanilla play through first with no mods, etc.