I'm mostly unfamiliar with the current offering of last.fm, but the name is familiar from way back. Glad to see something well-liked reclaim some independence.
At a glance, they're providing an interface to YT sourced content with some value adds around tracking or categorizing listening.
A quick question for users: can the site itself be configured as a listener without streaming / displaying the video? In general, YT has a lot of music, but the perf hit of streaming typically high-quality video as well is a blocker when doing dev work on my main machine.
You can toggle between YouTube and Spotify as the default playback provider.
Note that you do need to be a premium Spotify user for it to work. That's not needed for YouTube, so that explains why YouTube is the default.
I'd be way more sold if I could pass in a static dump of my library music and get a handful of suggestions to demonstrate value.