Get the Stalker complete Mods for all 3 of them.
The Stalker series is quite good, and the Stalker Complete mods do a pretty good job of rounding them out with bug fixes and some gameplay fixes, mostly graphical though.
http://www.moddb.com/mods/stalker-complete-2009
There is also one that adds random blowouts to SHOC and makes the game a little closer to the original idea but can't remember the name.