Well integrated with G Suite, and a free addition; Very extendable
Only intra-domain communications, "Not good enough" (yet?) to convince Slack users
After EAP, I am still very excited for this new Google Cloud product! Hangouts Chat will open up group messaging to a much wider range of organizations than before. (There are so many orgs that DO have & love G Suite, but don't use Slack on an org-wide scale. Yes, I know that's hard to believe for the people in this community. ;)
While during the EAP it was obvious why you couldn't connect to users from other G Suite domains, sadly that's still not possible. The integration with 'classic' Hangouts could be better too: Group-messages should sync as well, like the 'private' messages.