I'd advise playing it unmodded (especially if you like hard shooters), since Complete makes the games a total roflstomp. Vanilla Stalker (all three of them) is one of the best gameplay experiences you can have. Just compare the sprinting between the mod and vanilla, laugh out loud at the motorbike-speed sprinting and note how it isn't documented anywhere (at least not on moddb). I tried fiddling with the mods - changing ltx settings to 'my taste,' but they seem to be such that I don't think even artistpavel knows what he changed. Dumbed-down AI, altered ballistics (varied probability to hit has been completely removed lol), lollerskates sprinting (you can cross major areas in less than a minute without fatigue), fucked-up FOV, removed headbob, broken actor proportions, increased inventory limit and a whole host of other bullshit that isn't stated in the feature list, not to mention other stuff further in that I didn't see before uninstalling this heinous garbage. So I finally gave Complete a go for the first time recently and imho it ruins these games.
