It's still 100% an improvement over what we used for chat before (Skype), but I'd be much happier running IRC or XMPP hosted on one of our servers. The boss decided on Slack instead as it's less maintenance on my part. I don't mind the extra work involved with running something we control, but the company wants me on other projects.
The only solution on Linux that implements audio, video and screen sharing is Sky (http://tel.red/), and it's incredibly flaky.
It doesn't help that the client hasn't had much more than cosmetic changes in at least five years, and is largely abandoned for Microsoft's kludgey Slack competitor.
When something bad happens, usually it is network infrastructure related or some IT experiment going on.
Sometimes when trying to log in it would say that the (saved) password was incorrect, the user would go change it in their Microsoft account and it still wouldn't take it, then a few hours later it was working fine again.
Slack also has much better search, and their support for attachments is dead-simple. Sending a file on Skype was always a chore that felt like it was 1999 all over again, but on Slack it's literally drag, drop, and collaborate.
As I said before, Slack wasn't my first choice but it's a good platform for what it is. I don't like that our conversations and files are stored on their servers, but I doubt anyone at the company is sifting through our stuff looking for dirt or valuable info on a small business with 10 employees.