I like the story of the game, the challenge of the levels and playing the custom level/missions.
Played this game with my brothers, we always made challenge levels and labyrinth as a challenge and competition between us to see who could create the most challenging experience for each other.
The different objectives that could be assigned to the level editor was the most enjoyable part of the level editor function.
On the main story, I like the narrative and the different perspective each character had, and the diference in game play, the core mechanics stayed the same between each character, but each one had a mechanics ar type of missions that are explored in each route.
Having the game brought to newer systems and being able to play on computer would be really fun, specially with a possibility to share custom levels online, if that can't be done, creating levels locally still would be great!