This update is very disappointing. Laggy as shit on my 2011 MBA (which was zippy on ML), the inertia scrolling algorithm seems to have changed (for the worse), Calendar (like its iOS 7 counterpart) sacrifices productivity for aesthetics, Safari seems to drain the battery like crazy, Messages made my speech bubbles and those of the person I'm talking to the same color (without losing the gloss).
Half-baked update. Should've named it Liger or something, and then really ushered in a new era with the whole geography-based theme Mavericks is starting with an update next year to bring ALL the apps (except Calendar, eek) to parity with iOS 7.
Right now, it's an unsavory smorgasbord. With all this lag, I can't think of a single thing I'm really over the moon about except being able to reply to messages without switching my window (and, in theory, the new power saving features, but my battery life is shit no matter what and has somehow gotten even worse).