We can't compare leopard with lion, too long a generational gap, but we can compare lion to snow leopard, and besides lion fixing a few important security issues, I think a lot of people will argue that lion is a worse os than sl. Certainly lions adoption numbers despite it being pimped with icloud (my sole reason for upgrading to lion) and forcing a lot people to upgrade just to sync their devices, and despite it keeping a low price for updates, are still way behind sl. Mission control, monochromatic ui choices, versions, iOS elements, iOS looking applications, are at the very best dubious choices that a lot of people intensely dislike and I have yet to see a feature that people almost universally like and think it makes their computing lives much better in lion.
Lion has also been a very buggy release, and more often than not a slower os than sl. It's broken compatibilities with smb servers based on apple dropping the gpl 3 samba and writing their own buggy smb2 protocol, and it still didn't address one of os x biggest shortcomings that of resolution independence. You take simple things such as the finder and it seems nothing really enabling or creative has been done about it since leopard. And you still have that unruly monster of a content manager iTunes which is in dire need of some re-imagining.
Lion is simply not a good progress for os x, the things that make it a good os are the ones that made leopard a good os and for that matter snow leopard, lion's main strenghts are leopards strengths, and some underlying sl tech, and the things that make it a bad os are mostly "features" of lion. And it's a sham that mountain lion is touted for a reminders and notes app a la iPad Amd for a growl like notifications service a la iOS (a la android to be exact because we can all remember what iOS notifications looked like before...)..