Not to offend anyone, but Chrome major version releases tend to feel relatively incremental compared to what I had come to expect from Firefox.
Will be interesting to see if Firefox can keep to their new release schedule after 4. Otherwise it seems that Chrome just iterates to fast compared to Firefox. Chrome 9 is a long way ahead of Firefox 3.6, sure Firefox 4 might even it up but if every release has this kind of beta time Chrome will just keep skipping ahead.
I'm pretty sure that the reason I can't come up with the differences is that the change is so gradual. I know Chrome has been improving, it's just not a dramatic change like FF 1 to 2 or IE 6 to 7. But Chrome 4 to 9 doesn't even seem like a dramatic change. if they were using normal versioning, I don't even know if it would be time for Chrome 2.0 yet.
tl;dr Chrome's major version releases are supposed to be incremental.
Check the Wikipedia pages for each major browser to see just how much changed in the versions represented. (Perhaps I should link them!)