I used Cinnamon for a while and was quite appalled by the bad quality of their themes. The vast majority were just unsable, because of too small a contrast between some of the items, or just plain ugly colors.
Adwaita was about the only usable desktop theme and I used it for quite some time.
Then I switched my desktop back to XFCE. A significant part of my reason for this is that I make a lot of screenshots, and the screenshot program for Cinnamon just sucks. Too many buttons to punch each time just because it tries to "help" you and outsmart you. XFCE just has two setting screens for each screenshot. It first lets me choose what I want to make the screenshot of (whole desktop, window, custom) and then asks me what I want to do with it (Save, clipboard, or load in a drawing program) which is perfect for my use.
I don't like "Thunar" much in XFCE though. It's a pretty basic file browser, and it has troubles with recognizing file changes, which is quite annoying sometimes, but it does the job. Most of it anyway.
It also does not show file dates properly. When I've had a few compile cycles of some uC program, it shows all files as "today". What sort of idiot ever thought it up to make that the default?
I've also never had a Linux version that can properly handle modifications to mimetypes and associations of those with programs. There probably is some cli to do it, but I'd much prefer some mouse clicks and typing in a shebang for creating a new mimetype.
I don't care much for tweaking the UI and all the theme nonsence, but it has to be something simple and with balanced colors, and no silly mistakes with things that should be clearly distingguashable (such as the title bar and the menu of a program having the same color. The "Kokodi" theme works reasonably wel for me. It's somewhat similar to the windoze95 look I am familiar with.