Maybe its my nostalgia speaking, but I hate a bad guy who laughs, and from Beast Wars and on, Megatron laughs too much. And when I say 'hate' I mean it rubs me the wrong way when Megatron opens his mouth only to spill a bunch of giggles.
And Megatron needs a raspy voice. It accenuates the nasty battle scars he would have if made of flesh. I'm in the camp of the original G1 is better than any other. And the original movie is awesome, other than completely destroying Grimlock's character and making Ultra Magnus a complete nincumpoop. The image of Starscream frying and turning to dust while the crown tumbles through him will always stick with me. That and Optimus turning grey and the lights in eyes turning out.
Long live the 80's cartoons!