- It's slow on every platform I use (iOS, macOS).
- I often don't get notifications at all, on either platform.
- The Mac client crashes too often.
- The Mac client uses more resources than it should.
- Threads are useless.
- Settings are split into too many different views.
- I dislike the design. It's too spaced out (even with the "compact" setting). There's no dark mode. I don't like the icon. Everything is too cutesy.
- I hate the emoji. I don't want more emoji in my life.
Most of all, I hate the hivemind that says it's the only viable chat system, so much so that even open source projects use it over IRC. Hipchat wasn't too much better, but I've not gotten the chance to use it in the past few years because everyone defaults to Slack. I'd love to try Facebook's new work thing, but there's the same problem.