Ai is pretty bad, they don't even relocate after hiding to try to find you. in fact the Ai is my biggest complaint about the game. After an alarm, you wait it out and they go back to the same patrols. They hardly detect you in the idle state when other sniper games would have long since seen you.
physics: I tried to outsmart one level by moving a body that I knew would trigger an ambush but the body dissapeared off my back when I got too far away.
Optional objectives are mandatory to finish a map. Normally I wouldn't mind but when gameplay isn't interesting enough you just want to leave the area once the main job is done but you can't until everything is done.
Climbing and interacting: some key areas are glitchy and you can't interact quick enough or at all to avoid enemies or complete a mission. For example the final mission planting a device, the text to interact is overlapped with other commands.