Somebody needs to tell the people at SyFy that SHARKS DON'T ROAR! Almost every shark movie I've seen on the SyFy network lately contains roaring sharks that sound like lions--and those sounds were obviously taken from pre-recorded lion roars.
That said, the reason I'm giving this a 4 out of 10 because it's not as bad as "Sharknado". Yes, there is still--as in almost every SyFy movie-- some kind of disgusting & egregious use of pretty young girls getting all hot over young guys; SyFy just loves their pointless use of sexuality. However, at least the writing in this film's story isn't quite as awful as some other SyFy flicks. There are some (sort-of) likable characters and a decent story arc.
There is actually an okay story here; there's a decent beginning, middle, and end. Some like-able characters also sweeten the mix. Unlike "Sharknado" there are actually some well-edited bits of stock footage of sharks mixed into the film that don't look too out-of-place. The acting is naturally sub-par, but it's not total garbage. You can tell some of these actors at least rehearsed their roles and didn't push it or over-act them.
So while "Planet of the Sharks" definitely isn't the film you want to save for that special weekend night, it could be a good bit of entertainment to chuckle at with a buddy or your significant other on a rainy day. It is totally forgettable, but it's not so awful it'll make you angry!
4/10 for creative effort, some okay writing, and entertainment value.