Terminator 3 was a travesty primarily due to the incredibly lame and cheesy jokes, it wasn't even funny cheese like you get from the oldskool Arnie one-liners in Commando etc, it was just utter, utter turd. It's the most recent terminator film I've seen and yet it is largely unmemorable, I can remember much more of what happens in T1/T2.
Of course, I'll still watch T4 because hey, it's a terminator film. And in all likelihood it should have better plot and action sequences than T3.
Personally I think Terminator2 is possibly the best action movie ever. Die Hard comes close but it doesn't quite have the same scope, nor the same emotional impact. Scenes like the bike/truck chase and the assault on Cyberdyne Systems are as good as you will find and the whole thing ties together nicely.