Non-Russians really get shafted here lol. For those who don't understand Russian, my most recommended one is OGSE 0693, but others worth checking out right now are Spatial Anomaly (CoP mod), Valley of Whispers (CoP mod), maybe Lost World Origin for SoC. SoC has the best story mods, although many are also standalone. There are a number of good story mods, and a LOT of crappy ones. SoC received the most of the latter type of mod. Story mods = Mods that either tell a new story, or tell their own version of one of the existing stories. and Dead Air will be worth checking out too.
The only ones worth checking out right now are Call of Chernobyl by stason174 (my most recommended) and Anomaly 1.5 Beta 3.0, but the latter is a beta with a lot of issues. Forks of CoC have been made to expand on it. Call of Chernobyl started this but is no longer in development. Freeplay mods = the most common ones for CoP, these mods have no real aim or purpose unless it's just faction warfare.