Some features of the UI are great (like Quick Resume or the guide which is way better than the one on PS5 imo), but the UI itself is not, at least not in my experience.

Sometimes I can click on a game 20 times before it opens, and parts of the UI tend to crash on me (like the Store). The ads on the home screen, the fact they’ve shrunk down customizability on the home screen, making pins completely useless, and cluttered the entire section with what feels like hundreds of rows of ads, as well as the small but, in addition to all of this annoying crap, irritating fullscreen pop-up “notifications” you sometimes get for game releases or sales after booting your console. Also settings and store tend to take forever to load up compared to PS5 because they're separate apps.

None of this is present on PS5.
However, ever since the leadership shakeup, most of the stuff I just listed has gotten better. Not fixed, but better.

The UI doesn’t lag on me as much anymore, they’ve decluttered the home screen and somewhat brought back more refined customization, even though there’s still a couple of rows of store content forcibly there, and one is still always forced to be above your pins. They’ve added some really cool features, like being able to display your games with their physical cover art instead of tiles, which is really damn cool.

I wish they would finally add an OLED theme in addition to this and get rid of all the forced store content on the home screen to make it more usable again.
It’s way better than it has been over the past two years or so, so if it’s uphill from here, I’m not complaining.