I've seen it, and this is my review:
Mega Shark vs Octopus is a release from The Asylum, a movie studio devoted to making "Mockbusters", the very same studio who are responsible for such quality films as "Transmorphers", "I am Omega", and "Snakes on a Train".
Keeping with it's "Too awful to be a b-movie" tradition the studio has given us a film that will no doubt set the bar for all reviewers to rate crappy movies by.
Spoiler!
In a movie that gives Britney Spears a glimpse into her own future, 80s pop idol Debbie Gibson stars as Emma MacNeil. She is a rogue "by her own rules" marine biologist who receives the ire of her boss (a man doing his best David Caruso CSI Miami impression) for stealing a submarine to do some whale watching in Alaska.
While in Alaska she witnesses a US military mission to apparently plant some sort of sinister sonar device to destroy iceburgs or something. Its actually really unimportant because the entire movie is about demonizing the establishment and rings with a pro-environmental message. The soldiers could have jumped out of a helicopter, raped a dolphin, wiped their ass with a seal, used beluga skin to make themselves a new pair of boots, and it wouldn't have made much of a difference.
After the sonar releases the titular giant octopus and mega shark (megalodon) they make quick work of destroying tankers, jets, and an oil platform. Its bad CG. Like, really bad. As if you took a kid who was about to fail a high school computer design course and gave him this project to keep him from flunking. And clips are re-used again and again. I think I watched the same profile of the shark swim by the camera about six times during this movie.
A mix of stock footage and long shots of characters in deep thought pad a movie that, without these fillers, would be roughly 35 minutes of bad actors screaming at each other and crying.
Lorenzo Lamas enters the movie mid-way through as a racist military commander with a douchebag ponytail. These things give him character. These things make him tough. These things make me feel that he doesn't care about anything but protecting the free world from evil. These things make me respect him. Awesome screenwriting here.
After introducing a series of throwaway characters like Emma's Irish mentor (a man with an accent so cheesy I had to look him up on Wikipedia to confirm he really was Irish) and a Japanese marine biologist who dispenses fortune cookie sensei and manages to tap Debbie Gibson in a meager love scene set in a submarine the film progresses to a series of "showdowns" with the giant creatures in which the American and Japanese militaries are dessimated attempting to kill them.
Fortunately our plucky hero Emma is able to surmise that the creatures can simply work on killing each other in the north Pacific. After some horrendous CG and a failed mutiny by a sub pilot the mega shark and giant octopus go head-to-head and crush each other to death thus ending this painful experience for me.
The movie ends on a tender moment with Emma on a beach with her Japanese counterpart in a romantic embrace only to be interrupted by the obnoxious Irish guy who provides them with evidence there may be "another creature out there", thus ending the movie on a hopeful note that we may see a sequel likely entitled "Fuck you I'm not watching this shit, lets just rent Road House again".