About S.T.A.L.K.E.R

If you can't buy them all at once, follow this order: SoC, Clear Sky, CoP. Yes, they are totally worth the money. Also, install the Stalker Complete mod for bugfixes, better AI, graphics, weather and so on.

Call of Pripyat has the best general gameplay mechanics out of the three. But from a narrative perspective, Shadow of Chernobyl is definitely the best one to start with. And like Copper said, be sure to get the Complete mod or one of the other various total conversion mods. They make these games infinity more enjoyable.

Sweet, thanks for the replies guys :)

In my opinion Shadow of Chernobyl is best

Call of Pripyat. I played in the shadow of Chernobyl, but was not satisfied. in my opinion only the call of Pripyat is worth the time. Even a discount on it less and the price is more expensive.

Such great games. Definitely play them in order.

shadow of chernobyl.....believe me, call of pripyat is good, but "real" STALKER atmosphere is missing, and clear sky has lots of bugs(last patch fixed most though), SHoC is Real stalker....
but in my opinion all three are worth the money,

All STALKER games work great with Complete mods. Who would say no to a STALKER game? Bugs are to be expected.

Search the forum, you'll find tons of previous threads about it, and I have lengthy comments in several of them.