This afternoon I upgraded to OS X 10.9. After spending just a short while with it, I’m disappointed. I complained a lot to Baozi.
When Finder is in column view, sliding the Magic Mouse left and right produces this ghosting issue. That first impression did serious damage to my feelings for 10.9.
Same with Maps. The effect the map UI conveys is different from the actual result — you don’t get the effect you ought to when using it, it’s baffling, and I don’t even know how to pick two locations on the map and have it navigate. Back in the first half of this year I was planning to write a map app, but I dropped the plan when I heard the official one was coming. Had I known they’d crank out this piece of junk, I’d have built it myself.
Also, does anyone actually use iBooks? This update isn’t meant for us users in the Celestial Empire… With this kind of quality, I feel really let down now — my expectations were too high. I’ll spend the next few days back home seeing whether system performance has improved. If you want to do iBooks, Cook, you’d better get the iTunes Store into China fast.
Calendar/Reminders/Contacts have all been de-skeuomorphized. For now it looks off to me, and Calendar’s location and travel time aren’t practical yet in the Celestial Empire. 
Support for Tencent Weibo is exciting, but after logging in it feels as lonely as Twitter — Sina Weibo is still where the crowd is.
The main event — Safari is massively optimized. Never mind the performance boost: Reading List is finally not that old HTML format anymore, and the direct payoff is no more ghosting here. It has Shared Links like iOS 7 does, and I have to say, the continuous reading experience in Shared Links is excellent — as comfortable as flipping through a magazine. The feel of the Safari scrollbar has changed subtly too: the inertia animation runs longer and the easing algorithm feels smoother. 
Finder’s Tabs are okay. It’d be even better if they could do a column display like TotalFinder. Finder’s Tags are great.