The movie is wonderfully great.
If you enjoy the show (or have little ones who enjoy it), then everyone's in for a wild ride of the most extreme nautical nonsense outside of your small screen.
The creators, Hillenberg and Co., definitely made sure that what works in their 10 minute "shows" can indeed be extended into a 80+ minute feature and be so thoroughly absurd, wonderfully out of left field, amazingly silly, and excellently tailored to make you smile (a lot). How's that for adjectives?
Anyways, the beginnning of the movie is great, very "epic" and not even animated (on a side note, if you have the soundtrack, you'll find no Avril Lavinge theme song here) and very, very, very silly. SpongeBob and Patrick's journey is your typical standard "we must find the crown!" type of adventure, but the creativity lies in the way it's told, those silly characters that they meet, the songs that they sing (especially the ones with a certain type of "creature" - very silly), and finally, just the absurd absurdity that everyone working on the film works hard to achieve.
Hasslehoff's cameo is, by all means, not even over from what the trailers suggest. There's a whole lot more, and the scenes building up to that are incredibly tense and exciting, and the way they get to the denoument is great too. And the ending, wow, the ending, I can't and won't spoil it, but it has to be seen to be enjoyed (they also did this in an earlier episode, but it works sooooo much better on the big screen).
I love the show and now I love the movie. Highly reccommended.