I think it is not as much pure bugs as it is poor design decisions and console solutions that are horrible for PC that really drags this game down. Some of the design choices are simply flabbergasting.
* Displaying all the levels at the same time on the map (wtf)
* Not being able to bind skills to a button but having to use a skill then go to the silly consolish wheel-of-choice to pick another. Come on, that is just lazy.
* The minigames are just bad and a general skill check would have been more fun.
* Bosses that can take insane damage in a game that is set in a realistic world. That is so stupid it blows my mind. And to add to badness of the design, you made one of the bosses (Brayko) so hard that he is virtually unkillable for those that that go to Moscow first or create a character that is more into stealth than gunplay. This should have been solved pre-alpha, alpha, beta, whenever. The fact that something like this made it live makes me question what QA you have going.
* Not being able to set mouse sensitivity from within the game. In a PC game. In the year 2010. Seriously?
* Messing up mouse sensitivity for sniper rifle so that if you have normal sensitivity during the game you get hyper sensitivity for sniper rifle so it is impossible to target with it. When I moved my mouse 1 mm the crosshairs moved a quarter of my screen. I had to tab out and set my windows mouse sense to the lowest whenever I would try to snipe and the sensitivity was still too high.
That said, I had fun with this game and don't regret buying it. It does a lot of things right too. It is still a huge disappointment because this could have been a contender. Now it is just a 80/100 game that should have been a 90+/100 if they had someone making good design decisions. What should have been GOTY isn't even GOTM.
