The huge car chase scene probably makes this movie, with everything else paling in comparison. The sheer scale of the destruction is amazing. I haven't enjoyed a chase this much since Pierce Brosnan took that tank for a joyride in Goldeneye.
My main complaint is that with the change from Edward Furlong to Nick Stahl, John Connor went from being a whiny snot to a brooding snot, but remained a snot nonetheless. If Nick Stahl's John Connor tried to give me an order, I'd push him down and stand on his head.
If they do a T4, let's see John Connor be a bit more heroic, a bit more confident and in charge of himself. In T2, Connor was a marshmallow. In T3, they added a graham cracker's worth of hardness. But to lead like his character eventually must, you need to be a sword, not a s'more.
And let's forget the comparisons to Michael Biehn I've been seeing in the user comments here. The only thing Stahl's John Connor has in common with his "dad" is stubble and ragged wardrobe.