I saw the sneak preview today. To be honest, I was quite impressed. I was only marginally excited about seeing T3 and I got much more than I expected. Arnold still has it, to be sure, and man, that Kristanna Loken is REALLY FRICKING HOT. I'll be placing my order for 2 units when Skynet starts shipping.
All in all, it was 2 hours of crap getting blown up with a rather acceptable story thrown in. Left WIDE WIDE WIDE open for T4. Not that I would complain. Yes, some lines were reused but I felt they were done with tact and at appropriate moments. Very, very entertaining. I haven't had that much "fun" at a movie for a while. No thinking, no analyzing, just "BOOM!!" "OOOOH!"
I'll leave the "most disappointing sequel" to Matrix 2 (once the initial Cool Factor wears off it becomes a 2.5 action movie that has 2 hours too much talking) and the "most disappointing franchise" to Hulk (decent but very blhahhhhhhhha)