The main new thing in MV is the way they build hydroencephalitic headed cartoonish animation figures by adjusting the ears, the eyebrows and etc etc etc. They use 48x48 sprites now instead of 32x32. They also have side view combat back again.
You download other peoples javascript addins, same as for c2. MV runs HTML5 so the game can come directly off a website, no installation (just like c2). C2 is far more powerful than MV, but its going to be harder to learn.