Finally got around to watching this, 'cos I'm chasing the latest fads!
In the first half of the movie, we see a group of idiots go under water and immediately everything goes wrong as a meg escapes with no problems what so ever, then the Bad Guys do Bad Things because they are Bad Guys. Characterisation? Who needs it? Then in the second half, they repeat what many other movies have done and do "what if we increased the body count?" and here's an island to attack with sharks.
There's nothing new here that you couldn't predict from just guessing. Apparently this is based on a novel "The Trench," although I have no idea how much of an adaptation it was, especially as they needed to incorporate all the characters from the first movie... at least I assume so, I remember sod all of the first movie aside from it had Jason Statham and the young girl and basically has a lot of features China would like... that is basically this movie too.
Do I sound like I'm not impressed? It just had a hard time holding my interest as, as I say, it didn't do anything we haven't seen elsewhere. It's fine, I guess, but... it's just fine.