STALKER series.
The first two are really nice survival games where a single mistake can have dire consequences. Get caught in a gun fight and watch your ammo deplete whilst you are hitting at nothing, just trying to keep the bandits at bay, then out of nowhere you have a blood sucker decide to rip them apart for it's dinner and you run away grateful it was not you - just hoping you can reach a friendly area soon as you only have one clip left, and a single bandage.
I never finished the third, so I will not comment beyond it looks really, really nice.

I still want GOG to sell these wonderful games!!!!

book or game? :)

Well to be fair the book was 'Roadside picnic' (eh... Пикник на обочине), and while there was a STALKER movie, I don't really think there's Metro one

Stalker if you like open world games, Metro if you like corridor shooters.

Is it solely like Half Life in terms of gameplay or are there variations and "gimmicks" to the combat.

For example Crysis 1 has the power suit and linear but BIG wide open hub worlds and play the way you want (stealth or action)

Whats this game's features?

Few Metro books though and who knows, might be they very well make the movie eventually. who knows.

Anyways i like the original Roadside picnic book and the old Stalker movie very much. Ive only read the first Metro book, but it was pretty nice one as well. Different though.

About games, well i liked the first Metro more than Stalker. Stalker might be better with right mods though - havent checked whats the situation atm.

oh there is Stalker pnp rpg, but as far as i know Metro one is still missing :)

There's a bit more to it, there's some sections where you talk and buy and stuff. More resource management, the really good bullets that do more damage are your currency, so do you want to buy some stuff, or hit harder with the stuff you have?

STALKER no contest here.

For world STALKER
For story Metro
Both have amazing atmosphere and overall gameplay although Metro wins in graphics

S.T.A.L.K.E.R. if you like open world games with a lot of exploration. (highly recommended)
Metro 2033 if you want a linear scripted game. (so so game IMO)

And stop saying S.T.A.L.K.E.R. is post apocalyptic because it aint. ;P

Really beecaue the setting is Chernobyl after the nuclear disater and mutants all over the place and people trying to survive, that sounds post apocalyptic to :P

The Zone can be considered a disaster area, but the world around it is still intact, it has some similarities with Gorky 17 in that respect.

Localised apocalypse.

Pretty much, yeah. As far as The Zone is concerned, the world ended.