I'm yet to hear every track in full... I've listened to most of the OST though :3.
I find myself really favoring the latest songs in the soundtrack... So far (I think! I might be out of date T_T) there are 113 musics to listen to.
Yes! I know 10 is alot... and nobody is going to post in here :S... So I'll just make my list and get it over and done with (Sorry if I bracket alot ;3).
In no specific order:
1. Track 60 - Aeon.
2. Track 49 - Watery Grave.
3. Track 96 - Yetit Petit :3 (It's such a very up temp and pretty song).
4. Track 99 - Uncanny Lake.
5. Track 101 - Absolitude (Ooooh Only good sounding Harpsichord song in existence :3... If that's the instrument I am thinking of).
6. Track 104 - On your way back.
7. Track 106 - Sleeping Volcano.
8. Track 108 - Angelica (A cross between Trance and Futuristic Techno oooh~).
9. Track 113 - Monastery In Disguise (So very epic and full of sorrow ;_; ).
10. Track 92 - Naive Rave (Anyone who has played Ceres RO should know how mentally psychotic the constant Mini boss fights can become in the final floor of Lighthalzen Bio Lab... x_x; And then the true versions of them rush up to you and kill you in a second! Suits the place so well).