One good thing you can say about TPM is that it's prepared us all to not get too excited about Episode VII. Kinda like if you've been in one car crash, you might drive with a little more caution next time.
On the evidence so far, J.J.Abrams is a modestly talented Director with a taste for ludicrous scripts. But as with Star Trek you didn't care so much about the huge plot holes because you were having so much fun with a cast of great characters.
If he can pull off 'characters' and 'fun' he's already doing better than the Lucas' last 3 efforts. I hope ST Into Darkness is damn good, otherwise it's gonna be a worrying couple of years.
But what worries me the most is that Disney signed up the original cast and set a release date the instant after Lucas sold them SW. So basically the whole cast of elderly and now slighty rotund OT characters are going to be in VII whether Abrams can find a plausible reason for them being there or not.
Hamill had to be in VII. I think most of us have always imagined he'd be the new Obi-Wan figure running a reborn Jedi temple in VII. Mark's age will actually add to the depth of the character and story. But I can't see any good reason for the rest of the cast to be there. Plus you know Hamill's a fanboy like the rest of us and will bring his absolute A-game.