My main complaints are that the sound effects are really not great, mynoise.net is the gold standard in this space in my opinion, the rain doesn't even come remotely close to what mynoise has to offer.
An other issue I have with it are the not-really-adjustable drums. Their volume cannot be adjusted which is reather annoying since I have to decrease the main volume to about 1% and it's still too harsh. They also can't really be changed in a meaningful way. The default is okay for a short while, but I'd appreciate the drums to change ever so often. A nn guided drum machine would probably for the whole premise and be a lot less boring.
Now the main complaint: The melody. I set the settings to change, but the melody really doesn't. The blending is impressive, but there's just not enough material to blend together it seems. Music has such a wide variety of ways to make simple things enjoyable, interesting and generally nice to listen to, none of which are applied here.
Lesser things include the bright pink background the developers chose for some reason and made non-adjustable and the lack of tooltips, as well as the way too fast triggering of the movement of objects when I really wanted to change a setting. Minor annoyances more or less.
When I'm in the mood for lowfi, I open one of those youtube streams in vlc without video, then unmute the storm day noise generator from mynoise, really can't recommend the website enough.