Voyager, the last two movies (Insurrection: The plastic surgery villains, Nemesis: Isn't it fortunate we just "happened" to find this exact duplicate of Data? eh number one? *nudge nudge* eh?), and the first 3 seasons of Enterprise all did enough damage, thank you.
The spin-offs in general were not in keeping with the original series. TNG can be summed up in: "These aliens are trying to kill us, but we're "evolved" so we'll try not to fight back TOO much. Let's sit around and talk for 30 minutes, have a blab session with the Counselor *yawn*, then come up with some BS techno-babble solution to our problem, hit the reset button and do the same thing next week". TNG was good from seasons 3 on, but still suffered from these problems. The first two seasons are some of the worst television I've ever seen.
DS9 made great strides in returning to what made the original great: conflict among the main characters (something sorely lacking in the others), the notion that 300 years is not enough time to create a perfect human went out the window, and the characters were actually DOING something instead of playing chess with Whoopi Goldberg. They were still much too reliant on techno-babble and the reset button (nobody grows, nobody dies FOR REAL). I almost choked when I learned they were bringing back Dax in a new host.
The last season of Enterprise was quite good, IMO. The mini-story arcs, written by people who actually understood the franchise and helmed by Manny Coto, were top-notch. I especially liked the one with Brent Spiner as a young Doctor Soong and the beginnings of the Eugenics Wars. Voyager was an abomination.
The existing canon should stop at the end of DS9. Voyager and Enterprise canon (except season 4) should be tossed out the window. Lord knows how this new movie's going to go down, though it's safe to say that in their attempt to reach a mass audience it will not be a hardcore fan pleasing film.