This film certainly won't win oscars, but it's not trying to.
It's just having a bit of fun, silly fun, and for that, should be in your collection. Not all films need to be Goodfellas, One flew over the Cuckoos nest or Inception to be worthy. Films suit your mood and when you just what some brain dead silly entertainment, Shark night fits the bill perfectly. It's ideal for watching with a few friends over nibbles and beers. It grates on me when I go to someones house to watch a film and, on viewing their collection, realise it's only full of serious, worthy, intellectually stimulating films (I love watching this type of film in silence on my own). I don't understand the mentality of building a purely 'worthy' film library as, yes the films may have critical acclaim, but for watching with a few friends who want to have a chuckle, they'll kill the mood and make everyone silent. With Shark Night 3D you can chat/laugh and even throw popcorn at tv if you feel like it. The men and women are also in swim suits for most of the film, so there's eye candy for everyone too.
I gave it 4 stars because the way in which the sharks are used is sparse and not varied enough. You'll probably see half of the ending coming a mile off, but there are a few surprises.
The 3d is pretty good too, much better than expected. There is a great feeling of depth and the odd (very odd) object that flies towards you. It's a lot better 3d-wise than some of the 3D films I own, some of them big budget productions.