@Gargron As a slightly contrasting view, somebody who I really respect for creating great software and knowing how to persuade users said that the way to create something people truly love and want to use is to get the basics right, of course, but then to go just a little bit beyond that, do just a little bit more than they expect, and that is what they will love you for.
It doesn't matter how good the base is, you need the little extra that grabs attention.
This guy wrote one of those tilting-maze games in the early days of the iOS App Store. It was a nice game, but the thing that made people excited about it, that they kept commenting on, was that it was playable already when the main menu was opened over it.
Discovery is probably the biggest issue of Mastodon. It is really hard to find interesting people. Especially as new. You need to be motivated to stay like I was. For me it was open source. It made me look pass design issues like the 500 char limit.. I had also been looking for a good enough G+ replacement. I stayed because I was able to find interesting people.