You have to understand that there are only a so many shark movie scenarios that ever come into play.
1. Prehistoric Shark let loose by shifts in tectonic plates on the ocean floor.
2. Mutant shark as a result of nuclear waste of some sort.
3. Shark engineered by biological chemical testing.
4. Regular people put into scenarios where sharks happen to exist.
5. Supernatural sharks based on demons, aliens or whatever non scientific shark scenario you choose to subscribe too.
Now, only one Shark movie has ever been the first of it's kind to tell the tale in a way that kept people from swimming for many years, and that is Steven Spielberg's Jaws.
When this movie came out, it was the first of it's kind, and even though it was based on a book by Peter Benchley, Speilberg was a young director that clearly bit off more than he could chew. What saved his career, was using a Hitchcock approach to the appearance of a great white shark. You don't really see the shark until almost the end of the movie. Instead, you get the John Williams music, and the view of the shark from a first person perspective, and for all sakes and purposes, it saved the film, and history was made. However, the mechanical shark prop that Spielberg used was a nightmare from a filmmaker's point of view. Also...sequels to this movie were insanely bad. One movie called Deep Blue Sea was fun. It involved a group of scientists trying to find a cure for Alzheimer's using genetics to increase the brain mass of mako sharks. They managed to make the sharks smarter, and after a horrible storm, the sharks begin attacking the underwater lab, while trying to make a break for the deep blue sea. It's kind of a corny horror movie, but it is executed well...and probably the ONLY other shark movie ever made that is not a complete failure. Most other shark movies made past that involve regular sharks with regular people trying to survive. Anything else past that winds up in the bin of science fiction which usually shows up on the Syfy channel during the weekends. At this point, you just have to have fun with the source material. Most of these movie poke fun at Jaws and all it's terrible sequels. Some do it better than others. Somewhere during this transition is where my interest peaks.
Some of my personal favorites, whether they be serious or not include:
Shark Hunter (2001) Years after his parents are killed by a megalodon (an enormous shark that has supposedly been extinct for millions of years), Dr. Spencer is obsessed with the idea of hunting down and killing the monster. He's assigned to investigate the destruction of an undersea research station with the crew of the Argus, a giant submarine Spencer designed himself. After a little searching the team realizes that it was indeed a megalodon that destroyed the base, and the hunt for the creature is on. Will the Argus and its crew have what it takes for Spencer to get his revenge? Antonio Sabato Jr. and a pile of Hungarian actors. It is so bad that it's totally good!
Mega Shark Vs Giant Octopus (2009) The California coast is terrorized by two enormous prehistoric sea creatures as they battle each other for supremacy of the sea. A shark breaches a concord jet, and eats the golden gate bridge. Also Debbie Gibson as a Marine Biologist. Too Hilarious!
Sharktopus (2010) A half-shark, half-octopus creature created for the military, creates a whole lot of terror in Mexico while a scientist who helped created it tries to capture/kill it. This movie is just too funny to not watch!
The Reef (2010) A great white shark hunts the crew of a capsized sailboat along the Great Barrier Reef. Kinda scary!
2-Headed Shark Attack (2012) Survivors escape to a deserted atoll after a Semester at Sea ship is sunk by a mutated two-headed shark. But when the atoll starts flooding, no one is safe from the double jaws of the monster as it eats fresh delicious women and men. Oh Brook Hogan, is such an action hero when the shark attacks the atoll!
Bait (2012) A freak tsunami traps shoppers at a coastal Australian supermarket inside the building - along with 12-foot Great White Sharks. It's almost believable, and you won't hate the main cast this time.
Sharknado (2013) When a freak hurricane swamps Los Angeles, nature's deadliest killer rules sea, land, and air as thousands of sharks terrorize the waterlogged populace. This movie has set the standards of cheese, but has since then learned to wear out it's welcome. Tara Reid seems to be the last one in on the joke, and I don't know if that is supposed to be sad or funny.
Shark Attack 3: Megalodon (2002) When two researchers discover a colossal shark's tooth off the Mexican coast their worst fears surface - the most menacing beast to ever rule the waters is still alive and mercilessly feeding on anything that crosses its path. Best line ever: "So, what do you say I take you home and eat your pussy?".