Will Lion be Apple's Vista?
I installed Lion on a new partition on my iMac, because I was pretty shure, from all what i've seen about exposé/spaces, that it would really suck using Mission Control. And I was right, so now I'm back on SL and it's a great feeling that my trackpad does as I want.
For me, it's like Mission Control came out even before Mac OSX Leopard, for some simple reasons:
MC has one-dimensional spaces, and L and SL give you the possibility of using a 3x3 Matrix, which works great on a 27" screen. I can use the middle screen for my primary work, and the for adjacent spaces for other, less important suff, so using these 5 spaces is much easier then using 5 on Lion.
Then Lion can't show me all open windows at once, which L could and SL did an even better job.
When using MC, I can see my windows grouped, but if I've 3 Safari windows open and several other windows, I can't see all my windows at once, just the application windows.
While seeing all my spaces in L&SL, and using expose, I can see ALL my windows, and when I hit 'space' I see the a magnification of the app under my mouse, so when I move my mouse, in the same Space, it shows me every app. This doesn't work in Lion, I've to hit 'space' over and over again.
In Lion I can move a window from the active space, to one on the top, but not from the top to another Space, and 'expose'/MC works only in the active Space. On L&SL I can move apps from ererywhere to anywhere(exept when using multiple monitors, which still doesn't work in Lion).
So if you would explain the expose/spaces/MC features of L, SL and Lion properly to a complete outsider but in a random order and then you would ask him, which featureset is the oldest, and which the most advanced, than I'm shure nobody would consider the Lion features to be part of the world's most advanced OS. For me, and for anyone who truely grasps the functionality of SL's Spaces/expose, Apple has just done a giant leap backwards.
Last but not least, their highly praised MultiTouch gestures really suck (at least on a trackpad). When I first interacted with Lion, I felt like a CRIPPLE, because, nothing worked as expected, it was literally like where glasses which turn your world upside down.
The scrolling was inverted, which luckily could easily be fixed, then I could drag with tap to click and the trackpad prefs couldn't help


But then I found the checkbox in Universal Access, which is of course, the first place where any user, who's new to Mac, would go to find this setting

So how is it not a downgrade, if a setting moved from the most obvious place to an elusive place like being burried in UA...
When it comes to set up the different MultiTouch gestures, Apple clearly has gone rogue, because I think I was never that confused when using MacOSX, as I was while trying to find the best MultiTouch configuration. Under different tabs, you can set up different actions for 3-finger swipe and other gestures, so if first dragging is 3 fingers, then switching back/forward goes 3 fingers, then dragging is disabled, whitout informing me. Of course users should remember what the other setting are before modifing another, but in SL, I can't think of a gesture which could be used for more than one action, so why should a normal user start to worry obout such things. Well exept for 3 fingers, where I can choose between to actions, so in SL I see my two options and then I can decide, which action I wanna assign that gesture to. So why haven't they adapted this mechanism in Lion, have they gone nuts?!

The most obvious way for a normal thinking mind is the following, which is analog to how you can set up active screen corners in SL (so at least they once had this great idea of simplifying things): you give the user the possibility to assign an ACTION, to each GESTURE, instead of letting the used choose a GESTURE for each ACTION. It's so simple, 5 years ago, it could have been Steve's idea xD.
That way, the worst that can happen if you modify one setting, is that one action is assigned to 2 gestures, so at least no gesture changes it's action unnoted by the user. Isn't this genius?
Another thing is the 'shift' to an iOS lock, but once again they changed the wrong thing. For me, iOS has three main 'views' 1. Apps in folders, which is now LC (added), 2.Full screen apps (added), 3. 'task manager' where I can easily switch my apps (gone). Why has Apple removed this '4 finger swipe left/right' feature'? It was great and easy to use, I can switch to any open app with 2 gestures and a 4 finger tap. Of course I also could move the mouse to the dock and click on the icon, but 2 finger scrolling to the right app instead of haveing to move my eyes to the tiny icons on the screen edge is much easier
As for fast gesture combinations, I can see all my open windows with 2 gestures ( downleft corner for spaces and exposé, et voilà

This is de facto not possible in Lion.
So this proves that in several, IMHO very important aspects of Mac OSX, Lion is a HUGE downgrade from SL, and I really hope Apple reads this and improves Lion in 10.7.1 (which should not be that complicated
Of course other changes in Lion are great, but at least MC is a real Dealbreaker