For me, Christian Bale was probably the weakest link in the movie. I'm not a Bale hater by any means - I just thought he made a bland John Connor. I think I would've preferred they'd kept Nick Stahl, T3's John Connor. But on the flip side of all that, I liked the secondary characters a lot. Sam Worthington brought a ton of charisma, and I was pretty impressed by young Kyle Reese (who, strangely enough, is the same actor who plays Chekov in Trek).
So, yeah, I liked it. Lookin' forward to T5. Hopefully they give Bryce Dallas Howard more to do next time. I love her.