Mavericks introduced many clever performance efficiency techniques and very few gimmicks. Personally, I would consider Lion the worst release of OSX of all time.
It contained nothing useful, and instead we got clutter like social media integration, an intrusive notification centre, Launchpad (even more pointless than the already never used Dashboard) and a MAJOR decrease in performance.
Mountain Lion felt like a patch for Lions mistakes. Mavericks felt far more luxurious than either of the two and was very solid overall, in my personal experience.
Completely no sense: Lion introduced multitouch, iCloud, OpenGL core (it destroy Snow Leopard in 3D performance) and so many other things.
the problem users wants to whine... OS X is free, every update have new features and under the hood improvements, but if you read internet forums seems nothing works...
I'm working in a support center, never see a 10.9 to 10.10 Mac with wifi issue, as now the few problems i've seen were in router side. But naturally reading here it seems nobody with 10.10 can use wifi lol. Human race is lost.