I saw something a while back (don't recall where) about sequels. The author pointed out that while "part 2" sequels are usually a pale attempt to capture the spirit of the first film, there are a few notable exceptions (The Godfather, Star Wars). He did point out that without exception, part 3 movies pale in comparison to the original. I thought of an exception, though. A part-3 movie that was greater than the previous entries.

Goldfinger

Sean Connery's baby blue shortie bathrobe aside, the Bond films finally found their stride with this film.

I could probably say the same thing about Return of the Pink Panther, but it's hard to say what number that film is, given that one previous film barely features Sellers, and there's a dreadful version that has Alan Arkin playing Clouseau. It is the third film with Sellers playing Clouseau, though, so I guess you could consider it a part-3.