Oh man, now you've got me going on how amazing this movie is. The story behind it is the guy who wrote, directed, produced and starred in it (Tommy Wiseau, the weird foreign guy in the trailer) originally wrote it as this super serious drama...BUT...he failed at almost every level of script writing and the movie ended up being hilarious because of how badly it was produced.
So, he in turn re-branded the movie as a "dark comedy" but it was definitely written and filmed as a very serious drama. That's what makes it great...every scene is a lesson in "How Not To Film A Movie 101".