STALKER Shadow of Chernobyl had the best ballistics and damage system (enemies died when they should, guns handled not realistically but enjoyably), level design, atmosphere, story execution, and was the most moddable and successfully modded, hands down. Underground levels and inside levels were fucking nerve wracking, and encountering any enemy could be a surprising and deadly encounter. I still love to play it and hate every goddamn second I choose to scare the life out of me by doing so. STALKER Clear Sky had a working enemy cover system, omg, and enemies actually (very slowly and retardedly) tried to overtake eachother and control the zone. However this is dampened by the fact EVERY FUCKING ENEMY is marked on your PDA and the ballistics went from simple to noticeably crippled (dropping bullets at like 20m from assault and sniper rifles, overdone recoil, bullets looking like bolts from WH40K when fired, taking like 50 shots to down some stupid bandit etc), and that there are no competent mods that correct these stupid things. Underground levels were just tedious and repetitive, nothing new. Much better graphics than Chernobyl, but much much much worse performance compared to mods that make Chernobyl look even better. STALKER Call of Pripyat hits the worst FPS and gameplay performance I've ever seen. It takes all the ballistic and most gameplay mistakes of Clear Sky and translates them into a giant open field environment of randomly roaming enemies and allies. Despite how expansive and how much potential the levels have, they're less populated than the stalker camp at cordon in Shadow of Chernobyl. Amazing amazing idea and concept, but it's just not a "complete" game like Chernobyl or Clear Sky, it's got much to be desired, which modders can help with, but none have done a good job so far. All in all, if you're looking for one, get Shadow of Chernobyl, the mods are absolutely amazing and each offer a very fresh and different experience. Mods may never come to Clear Sky and are a long ways off for Call of Pripyat, as far as I know.