christian bale, sam worthington, and whoever plays john connors wife all give really good performances. especially worthington and yelchin. anton yelchin rules as kyle reese. common, moon bloodgood, and a few of the other supporting actors are really terrible. also i thought arnold's cameo was really well done! it wasn't bad CGI at all. everyone clapped in my theater when he came on screen.
I love Bryce, but her character (Kate Conner) got a grand total of two minutes of screen time, in which she did nothing of great importance. It didn't take a lot of acting skill to play that role. Anyone could've done it. I didn't think Moon Bloodgood was too bad.
Agreeance on the rest though. Sam and Anton were both great. Common was completely useless. When he and John/Bale were hiking that mountain midway through the movie (I forgot the exact lines), it sounded like he was going to start spitting a verse. Not good. The poor bastard tried, though.