Well, more than the UI, I feel that their song radio (suggestions) is disappointing, and I think this needs more attention because people keep falsely claiming how good Spotify'a suggestions are, but the reality is that you're actually missing out out on discovering new songs if you rely solely on their autogenerated playlist.

At first I too though it was great, but over the past couple of years I've come to realise that I've been missing out on so many good songs just because I've been relying on their radio. And it's not like these songs I've missed out on are obscure or not my taste - they're relatively popular songs and they fit literally smack bang in the middle of my tastes, yet in several years of listening to that genre radio, not once have I ever been recommended these songs - yet they're available on Spotify and even match the genre tags of the songs I usually listen to. I can't understand why.

So now I try and listen to regular, human curated old school radio as well, so as to not miss any gems that Spotify might miss.