Tracks like Otterly and Donimo, the last songs on the album, sound at once otherworldly and intensely familiar. Other reviewers have compared this music to the singing of angels, and that comparison isn't far off - it sounds like it's always been there, playing just beyond the range of your hearing as the sun rises (in the case of Donimo) or you drift off to sleep (for Otterly) or grin inwardly as you prepare a suprise for someone you love (Pandora, though oddly titled for it).
If you're new to the Cocteau Twins and looking for a place to start, "Treasure" is an ideal place to start as an early example of that distinctive otherworldly-familiar sound. If you're already a fan and looking for more, "Treasure" will be a welcome addition, as it combines the dreamlike vocals of Victorialand with the stronger instrumentations of "Milk and Kisses" and similar.
Frazer is the great unknown poet.
Guthrie is the metaphysical architect.
Do yourself a favor.
Buy every single recording they ever made.