“Megalodon” (** out of four) was a routine but reasonably reasonably well-done shark thriller about a military vessel (led by Michael Madsen) on the search for an unidentified submarine but soon find themselves besieged and attacked by a giant shark of whose proportions have never been seen or measured before. The kind of movie that gets bankrolled and made to capitalize on the success of a much more popular one (“The Meg” as if anyone can’t guess from its title) but this is actually faster and more fun but yet too by-the-numbers to succeed overall. “Jaws” still outchews all its imitators over 40 years later.