It's hard to explain what an absolute paradigm shift Gmail was. It was about as drastic a difference as you could have with personal email without altering the core service. Orders of magnitude more storage, completely free to the end user, a responsive and usable web interface, a single unobtrusive 1-line text ad when we were used to at least half a dozen that were often full-size banners or even popups, and a good search tool.
My wife (then fiancee) got us invites, and it was like Christmas. And all from the company that was way less creepy than Microsoft! I'm sure that part would never change.