Well to start off, for being a documentary basing the majority of its appeal off of nice narration by a very talented actor and 3D cinematography, this is as fun to watch as you would expect. It was definitely a nice thing to do on an afternoon with the family, and it really gives you a feel for underwater landscapes and the unique motions and routines of some random deep sea creatures. It is filled with entertaining moments, and you will really feel immersed.
The big negative for me was being somewhat ambushed by the global warming message several times when there was no indication to expect this (other than the seemingly true assumption that movie makers are propagating liberal political positions in titles that aim to draw children or families). I get that it is a theorized dilemma that means something to a portion of our culture, but I would also argue that it is widely dismissed among another portion with some sound, scientific reasons to form opposition. The point is- it has not been proved factual yet and has no relevance in a movie that touts a "fun" look at sea life. Plus, it is stated as fact several times during the film and implements the appeal of some heart-warming sea lions to sell the message.
Outside of this and the brief fish sex, it is a good movie worth watching. However, if you don't agree that CO2 is polluting and corrupting our wildlife, maybe give your kids a quick heads up before they watch something they may take to heart, as this film appears to have been made with that in mind.