As a new Mastodon user coming from Twitter, here is what I find most user-unfriendly.
1. Layout which doesn’t distinguish between original post and a reply to it. Very confusing.
2. Can’t figure out how to read a thread in sequence. Maybe my fault?

Twitter screenshot for comparison.
Maybe incorporate a few of the good design features of Twitter here? They didn’t get everything wrong!

Thanks to all for the suggestions! I’m trying Metatext and I like the layout better than with the Mastodon app.
I also tried Twidere but wasn’t able to display my own thread properly with that, and also it crashed twice.
I was attracted by the feature to post simultaneously to Mastodon and Twitter with Twidere though - are there any better iPhone apps out there able to do this?
@rahmstorf I configured cross-posting via https://moa.party so I can tweet and toot at the same time no matter which app I am using to do so.
Moa: Mastodon/Twitter/Instagram Crossposter

Link your Mastodon account to Twitter and Instagram