I think the reason people seem to hate T3 is partly due to the lack of James Cameron, and also because it was a belated sequel to one of the best Action-Thrillers ever made, and was therefore always going to have a lot of fanboy haters (and before anyone says "But it was rated 12A!!!!!", remember that it was still an R in the US and not toned down like Die Hard 4, it was just a daft rating by the BBFC). I think we'll see a similar fanboy reaction to the new Star Trek movie tbh.
Personally, i liked T3, while not as good as T2, it was still a highly enjoyable movie. And even though Arnie IS the Terminator, if T4 is set in the future then surely the Terminators wont be needing their skin.