Batman Arkham City - Finishing equals either:
1. Completing the main storyline
2. Completing the main storyline and all puzzles, side quests, and collectibles
3. Getting all the trophies/achievements
Again, I'm in the #1 camp, but curious what you and other feel equates to "finishing" a game. I know it's practically impossible to do option #2 for Skyrim though. Maybe the difference is "completing vs. 100 percenting a game."