1000 Misspent Hours doesn't like it and says,
To be honest, Creature from the Haunted Sea doesn’t work anywhere near as well as The Little Shop of Horrors, and it is often funnier by accident than it is on purpose. A lot of the gags fall rather flat, and derive most of their amusement value from the fact that somebody somehow thought they were funny.Million Monkey Theater says, "As with most every Corman movie, overall it's excruciatingly terrible, but there are some good moments of crackin' dialogue and inspired emotion. And it's a comedy, who knew?" The Spinning Image says, "It may look like it was casually filmed on holiday, but the movie is amusing enough, and doesn't take anything seriously." TCM has some information.