Surprised, I found MW2 to be one of the most broken games I've ever played. Everything about that game was mess. I remember getting it launch day, and within a day there was a ton of glitches and exploits. I remember the infinite supply drops. And thing is, you would think it would have been fixed and improved as time went on. But eventually IW just gave up.
The balance in that game was terrible. There were perks that stacked killstreaks, that absolutely destroyed the games balance. I remember the long barrel shot guns, dual wield and infinite sprint. The range on those guaranteed death across the map (okay not across, but it was fuckin absurd the length). Those, I know they nerfed. But it was some time.
And I just found the maps in general, to be poorly designed, in terms of spawn points, and how cramped they were. It was the first time where I felt in COD, it doesn't matter how good you are doing, you are going to die. Someone is going to spawn behind you. Someone is going to run into a room 3 seconds after you. I have fond memories of that game, and it's probably the last time I really enjoyed a COD game. But in hindsight, I really think it was a mess of a game, and I'm surprised they released it the way they did.
But I think there was some fundamental design choices that really couldn't be fixed.