Usually shark movies are fairly horrible, much like most zombie movies. And "Megalodon" is not really an exception from the standards of shark movies. It has everything you expect it would; fake shark and bad CGI effects. Check and check.
The story in "Megalodon" is about an oil drilling company which has built a massive rig which will revolutionize the oil drilling business. Being capable of drilling at depths which are previously unreachable, then they invoke the anger of environmentalists. Whilst drilling at over 5000 feet, they find a massive subterranean underwater cave which has a myriad of previously undiscovered aquatic creatures. But living in the cave is a massive Carcharodon megalodon.
While the story is straight forward and fairly generic for a movie of this genre, then the movie actually turned out to be semi-alright, in terms of being watchable and providing some entertainment for the audience. However, it just was bludgeoned to death by horrible CGI effects and fairly bad acting.
The concept idea for the drilling rig was quite good, and they managed to show it in a fairly adequate manner, although the CGI effects could have been better. And the combination of CGI effects and real props did work out well enough in favor of the movie.
While on the topic of effects, then I will admit that the luminescent aquatic creature designs were really impressive and looked really good on the screen. So thumbs up to the CGI special effects team on this achievement.
"Megalodon" has no one familiar on the cast list, and I can't really claim that people were doing great jobs with their given roles and characters. Now, whether this was the fault of the restrictive script or the talents (or lack thereof) of the actors, I do not know.
"Megalodon" is not an impressive movie in any way, and it is the type of movie that you watch once and laugh about it, then never put it back in your movie player again. For a shark movie, then this movie was lacking action, shark attacks and the sense of fear, that we saw in "Jaws", for example.