Long form: This summer had several movies that I was looking forward to. Most of them were either minor or major disappointments. So I went into T3 with fairly low expectations.
I will certanly admit that T3 wasn't as good as T2 - those are some big shoes to fill after all. Still, it has a charm all its own. Yes, the plot does take a backseat to the SFX a few too many times. Though I can't agree with zonereyrie that it was "just a SFX wankfest", there was more to it than that. Though I liked the ending, I still felt like it was too abrupt, like they ran out of story just as things were getting really good. I might personally complain that there wasn't enough character development, but in truth this movie has quite a bit of it - I just happened to want more.
Still, the good parts in this movie are pretty darn good. The editing is nicely done, you are <Arnie>unlikely</Arnie> to be bored. The stunts are usually both fun and painful. I did find myself caring about the characters due to the character development that occurs, including them having some rather un-genre like flashes of intelligence they exhibit. The Terminatrix is cool, they did her SFX well, though I think some of her dialog wasn't so great. Arnie's dialog is cheesy, but usually in a fun or cool way. The movie ends on a very down note, and I actually liked that quite a bit. Though, as noted above, I think they could have done the same ending a different way, and it would have been better.
Overall this is probably the second best movie I've seen in the last 6 months. (X2 was better.) Still, I do think it was was slightly better than Matrix Reloaded, Hulk and 28 Days Later.