Revenge of the Sith was great.
Back to the Future III was awesome (best of the series).
I don't know how we're counting Lord of the Rings (as three movies or one) but Return of the King was brilliant.
I haven't seen Terminator IV yet, but I liked the third one fine.
On the other hand....
X-Men III sucked balls. Which was too bad because the first two were fantastic.
Batman and Robin was terrible beyond belief. Completely unwatchable (and I'm a huge Batman fan).
Indiana Jones/Crystal Skull was pretty lame. "Nuked the Fridge" has replaced "Jumped the Shark" forever in my mind.
JMHO, of course...

Back to the Future III was awesome (best of the series).
I don't know how we're counting Lord of the Rings (as three movies or one) but Return of the King was brilliant.
I haven't seen Terminator IV yet, but I liked the third one fine.
On the other hand....
X-Men III sucked balls. Which was too bad because the first two were fantastic.
Batman and Robin was terrible beyond belief. Completely unwatchable (and I'm a huge Batman fan).
Indiana Jones/Crystal Skull was pretty lame. "Nuked the Fridge" has replaced "Jumped the Shark" forever in my mind.
JMHO, of course...

But thanks for reminding me of a trilogy I really need to check out.
I like the mention of "Bill and Ted's Bogus Journey". I was thinking more about trilogies or series with four parts or more for this thread, but that's definitely in my opinion an example of a sequel that wrapped up its 'series' perfectly. 
