Mortal Kombat is my first go-to example for how to make a fun game-to-film movie that doesn't suck. I know it's not a great movie, but it did everything I wanted in a Mortal Kombat-type film while taking itself seriously but not too seriously (which was the sequel's biggest downfall, in my opinion, after losing so much of the principle cast from the first).

The main problem movie makers face, I believe, is the issue of interactivity. Video games are an interactive medium, and films are non-interactive. Translating one medium to another is very difficult to pull off while making a successful movie: pander to the players, and you lose any hope of the non-gamer audience enjoying themselves; pander to the non-gaming audience, and the people who actually care about the property will boycott your film in droves.

Ironically, my second go-to example of a film that got it right is Postal. For all of Bolle's cinematic sins, and they are legion, Postal is simultaneously enjoyable as a gamer film and a non-gamer film. It's Falling Down copied on Silly Putty and then stretched to absurdity, and I think that's exactly what the story called for.

I'll also give props to both the first Silent Hill and the first Resident Evil films. Both manage to be enjoyable, watchable films in their own right, despite drastic departures from the source material. The sequels, on the other hand...? Yeah...no thanks. :)

Edit: I also loved Final Fantasy: The Spirits Within but I feel it would have ultimately been far more successful without the 'Final Fantasy' label. Square created a breathtaking CG world with an awesome futuristic story of science, technology, and nature all intertwined. Divorced from the 'Final Fantasy' name, it's a technological marvel. Weighed down with the RPG license, however, it was almost doomed from the start. Such a shame...