Re: Avengers 2 trailer is out!!!
Also, the premise of the Avengers as the world's greatest heroes means that they often taken on planetary and cosmic threats... and such threats are rarely subtle. The Avengers haven't had, I think, that many complex villains: Kang is a conqueror, Ultron is a bloodthirsty robot, the various incarnations of Masters of Evil weren't truly subtle, too... And Thanos is, of course, omnicidal.
Of course, the Avengers have faced Dr. Doom, who is one of the most complex villains Marvel has ever had.... but the movies can't use him, because he's part of the FF franchise :(