If you don't have plans to see this movie, you can check the spoilers here and then come back.
This one is a bit tough for me to assess since I'm not really a horror/schlock fest connoisseur, but I'll do my best. It's a solidly entertaining movie that delivers on what is advertised: An over-the-top carnival of flesh, gore and special effects with plenty of sharks. It's actually a decent cast of young actors, many of whom I've seen deliver in meatier roles, who move the bare bones plot along fine but don't quite give us a reason to care as they're getting slaughtered. The story is minimal, but it gets the job done; I guessed some of the big plot twist, but not all of it, so kudos there. The FX aren't revolutionary, but again, they impress enough and the 3D is well-done and well-utilized; there were at least two moments where I jumped a bit and let out at least a little yell because a jumping shark freaked me out. The sharks also looked darn scary and not done on the cheap, and at the end of the day I'm wagering that what a bunch of folks want to see here. Bottom line: If you were already planning on seeing Shark Night, you'll probably dig it; if you had no plans to check it out, I wouldn't go out of your way to alter that.