Since we've used Slack I feel more up to date and more in the know because I can keep up with what everyone is talking about. I have keywords that give me an alert when someone mentions my name or specific things in which I specialize. I've been able to quickly offer help to those who might not have immediately thought to bring their issue directly to me as a result, and have had the same happen in regard to problems I bring up in channel. It reminds me very much of hanging out on IRC when I was a teenager, but an IRC built for business.
Sharing files, code, screencaptures, etc is easy and intuitive. The integrations are useful: GitHub, Zoom video conferencing, Dropbox - having these items easily available only make Slack blend more seamlessly into my day.
I like Slack, and reading this blog post I couldn't help but feel this was more a mismatch for the author's use-case than a problem with the application.