Superfly - I will be the first person to admit that T3 is by no means a perfect film. It certainly has its flaws, and to that end, I do agree with some of the points that you've raised. But others, however, I'm afraid we're just not going to see eye to eye on ...
Firstly, I would agree that the plot of T3 is fairly similar to that of T2, in that John Connor and the Terminator are once again attempting to avert Judgement Day. What makes T3 different, however, is that the stakes are now much higher; in T2, Judgement Day wasn't set to occur for a number of years, whereas in T3, we know that our heros have merely hours to stop it {and ultimately even fail to do so}. In addition, all that our heros had to do in T2 to supposedly "avert" Judgement Day was to blow up an empty computer factory; in T3, they have to take on Skynet itself ...
Secondly, in regards to the early terminator models, you may be right in saying that they don't act like the terminators that we know and love, but isn't that the point? Aren't they supposed to be more contemporary, and thus more primitive in our view?
Thirdly, I don't actually feel that the humour in T3 was misplaced. Of course, not everyone is going to find "talk to the hand" funny {though I know I did}, but I feel that the comedy was a logical approach nonetheless. After seeing the lighthearted side to Arnie in T2, the producers probably felt that THAT was what the viewers would be most comfortable with for T3. And in any case, you still had the "evil" Arnie re-surface with much gravitas at the end ...
Fourthly, regarding Sarah Connor, what else could the producers really have done? Linda Hamilton had already refused to do it, and a decision to re-cast her for T3 might have gone down very badly with the fans. In any case, if we had had Sarah Connor in the film, she would no doubt have completely overshadowed the character of Kathryn Brewster, who {as Connor's future wife} we are supposed to grow to like. But I agree - perhaps leukaemia wasn't the best way to kill her off ...