I am not impressed. If I had used Vista as much as I have used Xp, I would be. Because it's really a gigantic step forward from Vista.
However having mainly used Xp, I'm not impressed. Windows 7 is still slower than Xp (not by much, but still slower). It fails to offer a good performing and good looking GUI. The aero interface is not only resource consuming but also very ugly. The classic interface is much lighter, but not any better when it comes to the look.
Things have improved. The Memory management is better than both Xp and Vista. (Though it still has some flaws)
The Security is similar to Vista, though UAC is certainly better (Though I don't think it'll take much time for malware writers to bypass it, like they do with Vista)
The new taskbar gets really messy with a lot of applications opened. But other than that, it certainly is better than the old Windows one. Nothing revolutionary though, being used to the Dock.
Aero Peek doesn't seem very useful to me. Hiding all windows is certainly better.
The Boot speed has been improved, yet much much slower than Leopard's (and certainly Snow Leopard's)
I like what they have done with media format support, though I'd never use Media Player. It's either VLC or KMPLayer for me.
I don't like having gadgets sitting on my desktop.
I don't like the Ribbon interface of the apps. Big fail.
And I don't like the "Editions" or Windows 7.
Overall, except for the slower speed, Windows Xp users should upgrade to 7. Though the process is quite tedious. In any case, Windows 7 is what Vista was should have been. Accept it or not, Vista users have been nothing but Beta testers for Windows 7. Well, at least Vista user's pain has has been paid off somewhat. No wait. That would've been if Windows 7 was a free upgrade to Vista users. And for Xp users, who were stuck with a 2001 OS just because there was no other choice.
In the very end, it's still Windows. With the registry, insecurity and instability it always had.