For example, I do quite a few code reviews on my Pixel 2, but what drives me crazy is that the lines in the diffs wrap! On top of that, the code font it uses is pretty large, so wrapping happens often and makes reviewing much harder.
The support for per-commit code review (which is only so-so in the desktop web experience) is even harder to use on mobile.
The main activity feed from / is nowhere to be seen, even though this is something I use daily on my laptops (long-standing pet peeve, since this is also non-existent in the mobile web view).
If you follow a link to particular issue comment (for example, from the bottom of a notification email), the Android app will just land you at the top of the issue.
So, having the app is an improvement over the mobile web experience (particularly since the PR review approval button was impossible to hit in the mobile web view without zooming), but IMO there's still a lot to be done here, and I hope they keep executing on it.