My biggest beef with Iron Man 2 was that they replaced Terence Howard with Don Cheadle. I like both actors, but Howard is much more suited to the part (no pun intended).
Also, I wasn’t that taken with Whiplash, probably because he was played by Mickey Rourke. I didn’t think he looked or sounded Russian, and I know some Russian speakers.
I have to agree with you about Don Cheadle as War Machine. I think Terence Howard would have been better in that role. Ah well, not much we can do about that.