A fun game doesn't really need to have strong narrative Wagner.
For example, I play the hell out of Titanfall and I never, ever, ever,ever... touched it's campaign.
By nature, FPSs are designed to be FUN because of its game mechanic and competitiveness. Why do you think Goldeneye was so successful? Mostly because of its mp.
Quake series, Unreal series, Halo series, COD are all found to be FUN by their user base mostly/solely because of their mp and their tight game controls.
And "bad" is a very relative adjective.