It's not a great film, but nearly all of the Caverns Underground Monster flicks aren't great films. To the letter they are all low budget B-movie throw aways.
And this is no exception... save for the fact it has Wes Craven's name attached to it so people come in expecting something more... expecting a movie he directed and not one he simply produced.
But the monster is underplayed and entertaining. The tension is claustrophobic and done well, and ultimately it's an enjoyable flick.
Grant you, it's one of those late night insomnia flicks that you watch once and throw away, but it's entertaining enough for what it is, and what it is is a B-Movie that knows it's a B-Movie, that tried it's absolute best to make something fun inside the constraints of a B-Movie with all