I have been writing and doing a number of videos about the PinePhone on https://linmob.net.

There is not one interface, there are many. I personally like Purism's Phosh the best, as Plasma Mobile has had more problems for me. The typing experience is overall ok, but it's not fancy (no autocorrect on Phosh, no swiping on any keyboard). I think watching videos can help you getting an idea on that.

What needs to improve? Overall reliably. I've inevitably always run into slowness and lockups after some time (postmarketOS Phosh did best, I could go a week without reboot). But things are slowly coming together, even video acceleration is coming with a future GStreamer release.[1]

[1] http://briandaniels.me/2021/06/27/hardware-accelerated-video...