I would say at least the Finder in Mavericks is "buggy as hell"[1]. It looks like it has a real issue with preview images (when the file is dragged to another window), Applescript, and updating based on file system changes.
Mavericks is absolutely a regression. My Mac Mini i7 (2013), for instance, will regularly recover from sleep with a black screen. Now if you are careful you can log in (hope the context is in the password box, type your password and return), but this has been there since Mavericks release. Many people have reported it. Still there. It is among a long list of bizarre oddities and system quirks that simply didn't happen pre-Mavericks.