It's an almost straight port of normal android into the headset which is at least familiar but they've really not made any progress in making it more VR and comfortable over time. Lots of small tweaking of whats probably not a great overall fit for VR.
For a direct example look at the room boundary system and setup.
Even with the new depth sensor and the color passthrough, it fails to figure out whether a table is a surface or a pillow of polygons, it fails to set reasonable wall boundaries (and then the ui is awful for addressing that) and then it nags and irritates people with those failures and misunderstandings.
Last I checked, the room software still only stores one room in your house. If you go to your kitchen for your coffee... remake the room boundary over again.
This is very fundamental for any AR to be built on and its terrible and unreliable.
Edit- also, last I checked, if you turn off boundary nagging with the devtools you cannot use the passthrough mode whatsoever.