[notahacker]

I mean, apart from anything else it's literally exactly the same issues you were highlighting with email: unnecessary verbiage to warm the discussion up and copying in loads of people indirectly involved, which may or may not be related to internal politics. And the fact the discussion which actually resolves the issue often won't take place in the channel.

With Slack you've got the added irritation of an expectation of real time responses, especially when someone's @mentioning the boss or everyone else in the division a minute after you haven't responded...