Well, there is the Priboi Story mod, which sets the story about 1 year after the event in SOC. You play a ukrainian military special investigator on the track of a secret group related to the recent events in the zone.
It has its flaws, and can be disappointing at times, but it integrates certain elements from famous mods like AMK (cars, new weapons, cut ouf monsters, deadly zone blowouts) while giving a not professional but still enjoyable storyline.
Some of the scenario can be screwed by entering the areas in the wrong order, so you'd better read a general walkthrough before you start, if you don't mind.