How do hour long shows like Law and Order or Star Trek have movies? Like...the show is an hour long! Isn't a two hour movie basically the same thing as a two part episode? Because both those shows have two part episodes already. I'm sure the movies have better special effects and scripts and such, but I'm also sure some people prefer just watching a two-parter.
I think the idea of a movie works better with shorter, half-hour shows, like DuckTales or whatever. That way, there's more of a difference between the movie and normal episodes. A full-length movie of a half hour show is like getting four episodes at once, with no commercial breaks, which is sweet.
I'm not sure how to feel about shows like SpongeBob Squarepants, which has full-length movies and made for TV movies. The more recent SpongeBob movie felt just like a made for TV movie to me. That didn't mean it wasn't enjoyable. I just don't know if it was different enough to justify the switch from TV to movie theater.