For example:
* Does not make it clear it's a point to point mapping (on iOS) right now. I discovered this the hard way.
* Unclear failure modes (see above). It's entirely possible to have messages be silently dropped.
* Texting vs. call methods unclear. I.e. there's a phone icon but no text icon (select name instead).
* Contacts list has some text only, some phone only, some both.
* The whole contacts list arguably needs to be rethought. It only shows others that have installed Signal/RedPhone/Textsecure. There is no easy way to see if someone does NOT have Signal installed and have the functionality to send a link to invite other person to add the app. I think this would help tremendously in the virality of the app.
* There used to be easy ways to invite people to the app within the app, seems to have gone away with only a tweet an invite to app store function remaining.
* There have been several instances when I can't see someone after they install Signal. They have to initiate a message to me in order for the contact to show up in the list.
* Signal has poor handling for contacts with multiple numbers. It's not clear which number is being used and you can't switch selection of numbers.
So what I'm saying is don't necessarily ape what Telegram/WhatsApp etc. is doing but I think Signal would do well to study hard the onboarding workflows of those apps.