Actually pretty entertaining. This movie doesn't ask you to take it seriously; all the characters have Western Movie cliché names right out of a Blazing Saddles type satire. What's odd is the attention to detail for the Western movie half of the story. You've got everything from gunslingers to saloons to spittoons to high stake poker players aiming guns at each other while they declare their hands, and so on. The sets, costumes etc. are reasonably authentic, more than one would expect from a movie like this.
The other half is the mutated creature portion, which isn't put together as well, but the whole package woven together somehow works. That's not to say the story is entirely logical; plot holes abound. The origin of the snakes and why they behave as they do; the movie doesn't really explain, or even seem to care. The whole focus is on a town full of cowboys having a shoot out with the massive army of snakes, and on this silly level, it succeeds as entertainment. These battles are sent up with reckless dedication to outrageous fun: how often do you get to see somebody blasting thousands of snakes with a Gattling Gun?
You know who's going to get croaked long before they do. The characters spout off comic one-liners when they should be terrified. The snake seen at the end looks about as real as a stick-man drawing. It's wacky, but a lot of brainless fun.
