The only positive thing I can find in the new update is that the desktop client is finally working fast again, after about an year of it slowing down after you delete a couple of songs in a big playlist (by big I mean over 100 songs).
The bad things:
1) When clicking on an artist, you're not sent directly to their discography any more, you're sent to an awful page that has existed on the website version of spotify for some time and need an additional click to reach discography. The way it worked before was perfect, a single page that had top 5 songs, followed by albums / singles, followed by all albums/singles artist appears on. Really hope this change will be reverted.
2) You could previously filter in the "add to playlist" list with keyboard inputs (information not shown anywhere, by the way. I stumbled upon this by accident). You can no longer do this. This is a straight downgrade.
3) The search bar in a playlist. It used to be ever present, and persistent. Now it is always hidden, the button for it is on the opposite side of the playlists and if you filter in two different playlists, it forgets what you filtered in the first playlist. So if you want to search for something in a lot of playlists, things got more difficult, annoying and tedious. Hiding the search bar behind a button is an anti-user move.
4) The artist column no longer exists, and artists are now shown under the song name, just like on the website version of spotify. If you want to filter by artist you have to toggle through the title filters first. There was always enough space in the desktop version for all columns. I don't understand this change, as the user still has no control over how long each column can be.
5) Tooltips no longer work. If there's a long name for the song name or album, you're out of luck. The only way to learn it is to click on the song / album and go to its page.
To those that want to go back, you can edit the "prefs" file found in "C:\Users\<user name>\AppData\Roaming\Spotify" and add the line "ui.experience_override="classic" to get the classic UI. Cheers to user AeroZ that shared this solution on another thread.