Call of Duty Modern Warfare 2, Call of Duty Modern Warfare 3 and Call of Duty Black Ops all run under Windows 7 on a Mac Pro.
Mass Effect and Mass Effect 2 run, although ME2 has some artifacting. ME3 won't run because Origin is required to run it, and Origin has problems in Parallels.
For the record, the error I see when trying to launch ME3 from within Origin can be found at C:\ProgramData\EA Logs and is:
I have contacted EA/Origin customer support about this, but they do not support machines running in virtual environments.
[06:33:38]------------ Opening Log --------------
[06:33:39]License Failure 3
As a test I found a cracked copy of ME3 which launched and played fine. I also play the copy of ME3 I bought in Boot Camp, so I know the issue is Origin and not ME3. Unfortunately this means any games which are Origin exclusives won't be able to run in Parallels.
If Parallels could fix this I would dance in joy.