You've read the plot summary, so I'll skip that part. Let's open the show with a few glaring flaws.
First off, the family moves into a house in the middle of nowhere, opens a sealed door they find hidden behind a cabinet, and discover they have a basement. None of that's so incredible, but Dad apparently has no problem with the fact that there's a gaping, monster-sized tunnel in one wall.
Secondly, monster mobility. The thing can apparently only manifest itself in three places: the house's cellar, a water-filled sinkhole that connects to its basement warren, and a dry oil well. It's allowed to come into the house by the rules of the film, but apparently only if someone opens the cellar door for it. What prevents it from crawling up out of the sinkhole or out from under the oilwell platform to wreak havoc in the open is never explained (my guess has a lot to do with the FX budget). And that cellar door? The one hidden behind a cabinet and ritually sealed by the Indians? Well, it also has a storm door leading right up into the yard, which isn't even locked.
Third, monster power. The thing's strong enough to overpower grown men with one paw and nearly pull limbs off trees, but it can't break down a flimsy cellar door to get at the goodies in the house?
All that being said, they did design a pretty nasty-looking beast, one that looks like a long-nosed version of the Terror Dogs from Ghostbusters (I call it Slime Rat). Unfortunately, they didn't have enough money to make a whole monster. Only the front half of it interacts on-screen with the actors, and it comes up looking pretty rubbery in close scenes.
It's okay for a cheap jump-at-a-body monster movie, and I didn't see the pacing problems that other reviewers have commented on. I think the key to enjoying this film is to be willing to let it scare you. Either that or ridicule it to death.
