I actually do think functionality has been lost. Calendar and Contacts are nothing like their Leopard counterparts. Mail has had several features removed from it; in Mavericks, you can't even display the plain text of messages. New and upcoming features are almost exclusively about iOS coupling, and have no real benefit to the OS as a whole; if I didn't know better, I'd swear Mavericks was Snow Leopard 2.0, with under-the-hood changes to tide Apple over another release, without any real functionality improvements at all.
Yes, Apple is more respectful to its user base as regards UI changes, unlike Micros~1. Yes, there have been VoiceOver changes for the better. Yes, you can now edit OpenDirectory using a GUI application. Yes, iCloud is sweet for contacts and calendar syncing. But let's be honest, are you going to miss that stuff? Really miss it? And is it not arguable that most of what you see should already have been in SL, or can be implemented using external services?
The real horror came when I tried upgrading my first MacBook to Lion, the last version it supports, and it ground to a halt under the memory strain. Think what you will of M$, but making sure their operating systems are long-term investments is something you could count on. Maybe it isn't true today, but I think the loss of SL is not dissimilar to the loss of XP on the opposing side. Both companies are trying their best to push us in the direction they think of as best, and we're not obliged to take the parts we don't like; with Apple, I fear it's just the lesser of the two evils right now.
And don't get me started on the way Apple locks its installation media to its machines, and even makes it impossible to use earlier media to perform an install!
Just myself, as usual.