This is a pretty cheesy movie, a poorly connected sequence of action scenes in CGI. On the other hand, some of those scenes outdo big-budget movies; I thought the outlandish street race in oversized video vehicles was better than the pod race in Star Wars I, and with a less annoying kid.
As bad as it is, it's all worth it to watch Rodriguez's commentary, to hear him discuss the process of making a 3D movie, the future of digital cinema, and how he saved money and made a mildly entertaining (and hugely financially successful) movie under strict time and budget constraints.
Some of my favorite parts of the commentary:
"We didn't have this animation done on time, so we just had the character complain how it looked like an old video game."
"I wasn't sure if people would get splitting headaches from the 3D, so I made the movie only 80 minutes. That way, if it was a problem, at least it would be over soon."
The funniest parts are slightly apologetic, but there's plenty more to learn from, and he's never at a loss for words. Unlike typical DVD commentary, there isn't any dead time while he thinks of some bit of trivia about what's on the screen.