What's the deal on end-to-end encryption?
Between this, Microsoft Teams, and Slack itself this is definitely a space to watch.
I'd keep HipChat in the running as well. It might not have all the polish of the competitors, but it's a straightforward, clean interface.
This isn't at all what I want out of Google Hangouts. I initially used it because it was such a simple, lightweight accompaniment to Gmail for business communication. The way the chat popped up from the bottom of the window meant it communicated passively when people wanted to chat quickly without getting in the way. The fact that the new design takes up an entire tab or screen makes it much less useful or usable for that simple use case.
But, fair enough, perhaps I'm in the minority and that's why they've changed.
OH shit, when's Slack going to publish another open letter?