Having just completed the expansion, I have to say it was quite fun, but one thing annoyed me - endles enemy respawns that happen far too often in realistically inexplicable ways. In particular, the endless respawns just before the map switch to Pripyat, on the Radar map. When the Duty team takes over the outpost at the top, and sits down by the fire, every few minutes the Monolithers teleport in again, and again, and again. They just descent from thin air. I would personally have much preferred for there to be no respawns of enemies (except maybe of monsters, but that should happen very, very rarely), since once an entire map is cleared of enemies and friendlies are holding all checkpoints, it seems downright ridiculous that 5 minutes (a trip to the bar) later all the friendlies are dead and the place is crawling with enemies all over again.
On a separate note, the Duty/Loner group in the farmstead near the Freedom base - they spawn when the player is in range (fair enough), but one of the people there _always_ spawns in the middle of the fire, and then just stands there until he dies - at which point all the other NPCs panic and start running around looking for monsters/snipers. It's a bit lame, and should probably be fixed.