Actually, some of the major plot points and themes were jsut like the games:
- The film was not set in any world any of the games had been in (except for X/X-2)
- The film did not use any major characters from any of the games
- The film did not use any 'systems' from any of the games ... heck, it didn't use a system at all
- There were chocobos (printed on Aki's cloting)
- There was a character named Sid
- There was the usual twist; the aliens were refugees, not invaders
- And the usual lineup of themes: love (Aki and Gray), adventure (save the world), dreams (which told the truth), life and death (everyone but Aki died)
Of course, Advent Children has more direct tie-ins than The Spirits Within. Consequently, fans didn't like TSW because it had little to do with the games, and non-fans didn't like TSW because it was incomprehensible to them.