Hmm, I think the separators between tabs in the new tab bar are too subtle, and overall it is too dark. The curved appearance of the selected tab also seems out of place.
edit: also, transparent elements with text on them? Noo! Maybe I am just sensitive.. I don't have the best eyesight, and I don't have the best monitors. In any case, I am thankful for Classic Theme Restorer, which someone mentioned elsewhere in this thread.