My main issue with Google Play Music is that they don't have a desktop app. I wouldn't even care if their desktop app was a wrapper around their HTML player. I just want keyboard music controls from my desktop and the ability to Cmd+Tab to the music app instead of hunting down the browser tab. Without a desktop app, using Google Play Music is disruptive to my workflow.
You can make any website a webwrapper "desktop app" using Chrome/Chromium's "Create application shortcuts..." in its More Tools menu. It just opens the website without any browser chrome, and prompts you to create a desktop shortcut for it. For a while, this was what Slack was recommending to Windows users for a "native" application, and it is still what they recommend to Linux users (see the bottom of the page here: https://slack.com/getting-started).
Creator of Radiant Player here. Performance and memory issues were a problem in the past and unfortunately have resurfaced in the latest release (1.4.0), but I am looking into them!
When did you try it the last time? I never had stability issues with recent versions. Sometimes (very seldom) it ends up eating 100% CPU, but restarting it fixes that.
Very nice app but I uninstalled after awhile because I want to get rid of Adobe Flash Player. It (the Adobe software, not Radiant Player) kept asking me to update itself...
It seems they are going out of business soon as the Auth API they based their business on is getting deprecated. :/ its moments like these where i hate how the web turned out.
On Linux, check out Nuvola player (https://github.com/tiliado/nuvolaplayer) - it basically wraps the web UI and provides integration with global media keys / shortcuts and the underlying sound menu (in Ubuntu). As a plus, it integrates with other cloud music streaming services too.
There's also Tomahawk (https://www.tomahawk-player.org/) but I found it a bit too buggy, and unable to canonicalize songs across the streaming music providers.