Gmail had an exceptionally well UI, minimal and highly usable. What is bizzare that mailers were extremely bad and you didn't even needed to compare them to Gmail.

JS had maybe it's share, but Gmail was minimal, condensed and fast. Literally no one had that back then and today no one knows because competition is dead. Now every webapp is JS heavy, but there is still a great difference in minimalism. Not saying that google products are small, but they seem to have a better balance in "fancy" user interaction than the rest of the web. The reckless transition to a modern web with more bells and whistles takes it's toll, mostly because "we can", but it should be "make sense here".