I think you're safe watching Iron Man, the Avengers, Captain America 2, and maybe GOTG (I haven't seen it yet, but I've heard good things). I would skip SHIELD.

I think you're safe watching Iron Man, the Avengers, Captain America 2, and maybe GOTG (I haven't seen it yet, but I've heard good things). I would skip SHIELD. It's just a B sci-fi series that's inflated by its association with the Marvel universe.