It's interesting that Teams is often compared to email or chat. It's much more akin to a forum or bulletin board system. I've found this to be a pretty powerful thing to have at work. However, it does happen to fit my work groups use case very well. We work on lots of short term projects. Each of these we spin up a "team" for. These are 3D projects that require a lot of media sharing from a cross disciplinary which works fairly well in Teams. It's been a pretty happy addition over Outlook (barf) and Skype for Business aka Lync.

Full disclosure, I work at MS. And I have never used Slack though would be glad to try it.