Weeeellll,,,,, let's just say that aside from the things that cause extreme "annoyedness" (Resume, Versions, Autosave, MobileBackups/Snapshots), I do like the new look of Mail. And I have turned off everything that can be turned off or tweaked - it still exhibits some really strange behavior. Other than that, not much change since I've decided to ignore most of the "features". It does seem to be a bit more responsive; that may be the 64 bit vs. the 32 bit and that may also be the reason for this: it is a memory hog; 2 GB is only good enough for say, Text Edit and maybe one other thing - if you want to actually do something, 4 GB would be the minimum and 8 GB would be good for iLife stuff. I've got 12 GB, so I don't have a problem, but kernel_task consumes close to 1 GB and Safari appears to eat RAM for breakfast, lunch, and dinner and uses it all after a while - I don't use Safari, but I've seen enought reports about it. And then there is the mysteriously disappearing hard drive space - I don't have that problem either because I don't use Time Machine and have MobileBackups/Snapshots turned off. Those features backup everything if TM is not attached and keep doing it until you hook it up. The ~/Library is now hidden - surprisingly, the System Library is still visible - go figure. In any case, you can resurrect it with a Terminal command and it'll stay visible. And then there is Rosetta - or, rather, it isn't there any more. So, no PPC apps. And my favorite iMovie version - iMovie HD 6.04 (old, but heaps better than whatever came later) is no longer supported I just learned; I'm currently trying to work with it - it keeps crashing, but still working when it's not.....
So, I've not made a final decision; I've partitioned my hard drive and have both SL and Lion. Will give it a bit more of a chance to hopefully get more options to control the truly annoying things (options are a good thing!) and whatever bugs out, but I'm absolutely keeping my SL partition updated.