thethingthatlurks said:
The original Call of Duty. It's bland, the characters are without backstory, there's the usual bit of destroying the entire German army on your own, and the levels suck. Wait, there is one quite brilliant exception: the first level of the Soviet campaign in Stalingrad, even though that was hampered by the fact that you're the protagonist, ergo you would make it across the Volga unscathed. Still fun for blowing off a bit of steam every now and then...
I actually consider it the best, and it's the only game I'll ever quote a Eurogamer article on (we fell out after they called both Mafia games GTA clones - yes, they're that stupid):
http://www.eurogamer.net/articles/call-of-duty-retrospective
The concluding paragraph says it perfectly (this was written around MW2's release, just for context):
"Never mind the fact that they might have just made the biggest-selling videogame of all time. Playing the original game again, I feel like this series could have been more than that."