I really enjoyed the STALKER games, but I think the combat system would need a lot of work to be more fun. There were some mods that addressed (what I would call) the major issues with the original games, but I'd much prefer the entire system to be rebuilt from the ground up to be much more like ArmA. Not necessarily one-shot kills, but definitely no more than 2-5 rounds to put anything down. Perhaps 6-7 if an enemy is super-powerful or wearing top-tier armor.
For the "otherworldly" creatures, they need variety in their behaviors. Something other than "notice the player -> get'em". I always thought how absolutely engrossing the game could be if you needed to track and study anomalous creatures, learn their very alien habits, possibly even create an ecosystem players could use to their advantage. The game is just begging for it, and we've definitely got the technology now.
