Just been to see it. I strongly recommend you go see it, it's awesome. A special effects extravaganza from the very beginning as predicted, but Arnie steals the show with some great comic moments and the female Terminator works really well. And she's gorgeous!
It's crap. Compared to the other two (especially the first) it's just terrible. Same old plot line. It's all special effect. Does that make a good film? Not IMHO.
It will make a packet though, as Arnie films usually do.
Watched a pirate copy a couple of weeks ago - it's good but not outstanding. Plenty of humour in it and the chase scene is something special (and very destructive).
It's definitely the funniest film in the series, though thankfully not the point where the humourous bits just make it silly. Lorry/truck chase scene is incredible, I preferred it to the Matrix one as that wasn't "real"