I think the Buzz Out Loud crew summed it up best when, in their Snakes on a Plane Premiere Video Special, they called the movie: "Awesomely awful".

But if you've made the conscious decision to see a movie entitled Snakes on a Plane, you should already be expecting that. It's fun, completely unrealistic, and just may get you to jump out of your seat once or twice. If nothing else, it's worth it just for Sam Jackson's infamous line.