When people say, "So bad it's good", this usually implies a lack of self awareness or skills on the part of the movie maker. Despite its flaws, you appreciate the effort or just laugh at the shear failure of the movie.
Here, with Unbelievable, we simply have a bad movie. There is clearly no effort to make an entertaining film. The cinematography is lifeless and cheap sets are frequently hidden by close cropped shots. The script has no spark and less humour, it's criminal to even mention Airplane in comparison. The level of parody here makes the likes of Meet the Spartans seem oscar worthy. You're pretty much left with a tired series of "naughty/lewd" (dead on arrival) jokes that have no set up and are limited by PG-13 restrictions. Beavis and Butthead did it better and with surprisingly infinitely more class.
So what are you left with? A movie where you'll just spend the entire runtime wondering why so many Sci-Fi (and specifically Star Trek) actors signed up to be in this film. Given the budget it's clearly not a massive paycheck although I guess it's a bit more than they'd get via Cameo.
You'll be better off just cruising IMDB and looking at their profiles. It'll be a lot quicker, cost you nothing and it's likely to be funnier.
