My (probably incomplete) list:
- Don't take 10 years.
- Moar music.
- Don't take 10 years.
- Moar CG's.
- Don't take 10 years.
- Voice-acting.
- Don't take 10 years.
- If possible, differentiate the common events of the routes.
- Don't take 10 years.
- Give Akiha a f*cking happy ending.
- Don't take 10 years.
Go nuts.