Sure you're not just under exposed? I've been shooting on the 5D MII and 7D for two years and just started using the 650D and to be honest, cannot justify the price difference when it comes to video (judging by the quality I got from the different cameras)
i do not want post too much offtopic, but no, sometimes i try in same position with different expo and settings, and all off them are bad, i think im too lame or this one camera i have a bit worst than other 650ds - or both.
and for example my 650d never shot 3 pic in a row in raw, only 2 and then wait - the factory description say 6 raw in a row.
i think this example what i cant do in wrong way...