It's quite nice, really. Good enough for us to drop Slack. Google is slowly replacing all their messaging products with this - Hangouts for GSuite customers is going away, and presumably this is why they drop the Voice integration.

The way they do threading - everything being a thread, at the top level - is more natural than Slack's.

Collaboration with external teams is seamless, you can add any GSuite or GMail accounts to a room. Much less annoying than being logged into a dozen external Slack workspaces.

Automatic permission management for Drive docs. Drop a link into a channel and it'll prompt to auto-add the right permissions that give everyone in the channel access.