Fantastic, been waiting for it. Features I have been looking forward to are message tagging and saved searches. What I consider the essential add-ons (Enigmail, Lightning and SmoothWheel) already work with 2.0, so no pain for me there.
The look and feel got an update too. The new theme is moreÂ refined, but perhaps a little duller compared to the previous version.
Without further ado, the links: