Frankly, I've been disappointed.
First, the color scheme is too drab and gray. Colors make action buttons stand out... now everything is gray...Gray scroll bars without a hint of gradient or 3D effect, gray search bar in Safari, gray Finder icons, gray linen at the login screen... even Windows Aero looks more interesting and inviting now, and I thought Apple really had it over Microsoft in the design department. It doesn't look good in an Apple Store to see so much colorlessness all around you.
They've tried so hard to lure iOS users in and adopt so many iPhone and iPad features that they forgot that a computer is NOT a portable device. What's so revolutionary about LaunchPad when the Dock already did a fine job of accessing applications? Mission Control is a nice idea, but it looks too jumbled and messy compared to Expose. It makes sense to have disappearing, unobtrusive scroll bars on a mobile device with limited screen real estate, but it is really necessary on a desktop or notebook computer?
There are way too many gestures that don't do much besides scatter windows around, and the trackpad gesture I used the most, four finger swipe for the App Switcher, is gone!
If you try to make an application full screen on an external monitor, it shifts back to your desktop screen and goes full screen there where I don't need it. This is a serious flaw for those professionals who use dual displays for their work.
And now I have to buy a new copy of MS Office because the PPC version is no longer supported. Why couldn't Rosetta carry over to Lion?
It's dismaying that the "revolutionary" new features are those that just serve to replicate a mobile device while the truly useful features have been overlooked or eliminated. I love Macs and every version of OS X that has been released, but I'm really underwhelmed with Lion. I hope that future updates will fix some of these things, but I'm afraid other things are here to stay.