1) The Empire Strikes Back
This is my favorite of all the Star Wars movies. It just worked so well. It was action packed, it had a lot of character development, and even though I knew Vader was Luke's father before I saw it for the first time, that reveal was still intense.
2) Lord of the Rings: Return of the King
I suppose it's technically a "threequel" but, the Lord of the Ring movies got better as they went, and this is one by far the best. I wasn't even mad at the movie's 10 false endings.
3) How To Train Your Dragon 2
The animators that worked on this film do not get enough credit. The way they aged their original characters was flawless. It was so detailed and I'm glad they decided to bump them up into their 20's instead of leaving them as teenagers. The score was still beautiful, and the story was even more complex.