Stand-alone CoP A.I. and a-life (simulation) overhaul revamping and radically improving every aspect of NPC and mutant behaviour in-game. Changes include everything from complete smart terrain revamp (spawns, function, logical repopulation of all quest-related places), thru NPC and mutant daily behaviours to rank-specific combat skills and habits (diversified aiming skills and reaction times). All this done for all locations (so Pripyat also got completely overhauled) and perfectly integrated into the storyline and side-quests meaning that (despite such major changes) everything works fine and doesn't get broken. No other CoP mod ever has touched this subject in such a complete and complex manner - and all this is available to you in stand-alone, 'vanilla-oriented' package making the mod easy to add to your favourite compilation.
Great mod, this is what Call of Pripyat needed! It's hard to go back once you've played with M.S.O.