The STALKER series may be on indefinite hiatus, but you should be able to get your fix somewhat with CryZone: Sector 23, which also takes place in "The Zone" and takes direct inspiration from the series in many ways. CryZone started as a mod, but has very recently converted to full-on independent game status.
What does this mean for you, exactly? If you played the original Dear Esther mod versus the final "game", that should give you a good idea of what to expect. If not, well, just know it'll be semi-professional work versus amateur stuff, so likely improved graphics and all around more polish, plus maybe extra content and whatnot. Oddly though, the game will still be free.
CryZone was first developed on CryEngine 2, but has since been moved to the new and improved CryEngine 3.
Hit the source if you're curious for more 'tails.