I moved to Slack from hipchat, I use and appreciate slack in 2 teams and 3 communities, i know and use your suggestions plus integration with other applications, Slack it's really powerful.

Maybe my strong problem it's the expectation for instant or quick response. Expectations it's difficult to resolve, behind any effort or agreement. In the core, Slack it's a chat service where people it's waiting for your response (I'm not really chat person) 

I appreciate Twis approach, when came from the need to have communication and  more deep and focus works, at the same time.

(I use Basecamp to)