More than just being a really conveniently large email system, Gmail is also a major step forward for webmail. It’s all run via JavaScript (or ActiveX for IE users), and thus you can use things like hotkeys. Just press “c” to compose an email, or g then i to go to your Inbox.
It also pulls away from the tired, inflexible “folder” paradigm to a label/metadata system for organizing mail, where you give your emails labels (for instance, I have “Friends” and “Politics” as two of my labels), and you can then sort and view based upon assigned labels. You can give emails more than one label, so you’re effectively “filing” the mail in two different metalocations.
It also includes spellchecking, is totally cross-platform (Safari, Firefox, IE, Mozilla all work just fine), and is beautifully minimalist in its appearance.
Even for folks who don’t have Gmail, it may be something of a boon: In order to respond, Yahoo! and MSN Hotmail have had to up their anemic disk space allotments.
All in all, I’m loving it.