Plan 9 rules! It has a gee-whiz sincerity that is utterly lacking in TF2. While TF2 is rambling, incoherent and offensive in a myriad of ways, there are worse sci-fi movies out there:

Battlefield Earth is the worst one I've seen so far. I can't imagine that John Travolta took much liberty with L. Ron Hubbard's original novel, since the movie is basically a love letter to his spiritual mentor, so I'm guessing the plot issues stem from the source material not the adaptation. A sample of the insanities:

1) Okay I get that (SPOILER)earth was conquored in minutes by an advanced alien race called Psychlos, but nothing any of them do in this movie convinces me they are intellectually superior, like it says in the script. They are a bunch of bumbling idiotic buffoons who happen to have more advanced technology.

2) The Psychos are after gold, and in 1000 years (SPOILER)of ruling over earth, they never bother to check Fort Knox.

3) The Psychlo security chief, Terl, trains one of the humans (SPOILER)to speak their language and fly their aircraft. Guess what happens by the end of the movie.

4) The humans eventually (SPOILER)rebel and manage to locate to locate a military base with fully fuctional aircraft and nuclear bombs, with the power still on after 1000 years.

5) And the stupisit plot twist ever, (SPOILER)the heros send one of their own to planet Psychlo with a nuclear bomb that ignites the atmosphere and destroys the entire planet!

BTW, I've heard rumors that Highlander 2: The Quickening is even worse, but I have yet to confirm it for myself.