I saw the movie 2 hours ago.
It was pretty decent. Christian Bale played a really solid John Connor. The story line isn't as "intense" as say, Terminator 2, but in Terminator 2 you also had to take a lot in because that's when they really developed the details about how the terminators travel in time, judgment day, etc. It's like Terminator 1 2 and 3 already had the bulk of the story line for Terminator 4 laid out. So having seen the previous movies, going into it I already knew a truckload so there wasn't a lot of gaps to be filled.
I thought it was solid. Definitely better than 3, even though I enjoyed 3, but I don't think any of them match Terminator 2. Terminator 2 will always stand out to me.
One thing I really enjoyed about Terminator 4 is the way the fighting styles were. There were a lot of scenes where you could see the way John handled an action scene and I would immediately think back to Terminator 2 when his own mother handled the situation in the same manner. I just liked seeing that indirect relation present.
My favorites of the Terminator series go: 2, 4, 1, 3.