Amazing environmental ambient music, this is something I often have trouble with. It can't be too memorable and the structure can't be too predictable or repeat in an obvious way - but it needs to be transport you immediately, be memorable in an undefinable way and when you hear it out of context it needs to put you straight back into the game. So much of this does this so well - particularly Lullaby of the Depths. The cello and strings kinda just meander around an ever-changing bed of synths, harps and decorative flutes - it's really well done.