I think it is a great leap forward, it's just that the improvements are in many areas where they aren't immediately obvious. Security has been the main development focus, and if Vista proves significantly harder for malware to infect, then that alone will be worthwhile. And search has improved beyond all recognition.

To an extent MS are constantly hoist by their own petard when it comes to new OS's - if they keep the look and feel of the UI reasonably similar to what has gone before, which helps folks who are already familiar with Windows, then everyone thinks that nothing much has changed. Personally I have no desire to go back to XP at all, I'm finding that I love Vista a bit more every day.