I think that a big part of the reason why Marvel: Agents of SHIELD doesn't work for me, is because I never had any fondness for Coulson.
I didn't notice him in Iron Man, I didn't realize it was the same guy in Thor until people told me, and so on.
I just always found him a bit bland, he doesn't really have any chemistry. he might work as the straight man in a sitcom, but even then, he'd only stand out, because he doesn't.
So when you make a guy like that the center of the show, you basically lose my interest, because there's just nothing about him that's in any way special. (it's also part of the reason why I never understood the popularity of the Clint/Coulson ship, esp. after Thor, when they'd barely even shared a scene together)