All the features that Slack offers are good to have, for example, voice and video calls, text messages, option to react to messages and direct reply to the messages, delete messages, easy to search text in conversations, pinning messages to be able to access them later, creating channels (groups), defining channel purpose, audience, privacy and visibility. Channel specific notifications can also be set. Multiple work-spaces can be added so that you can handle all the discussions from one place.
Also, its easy integration with other apps like Google Drive, Jira Cloud, Howdy, Google Calendar, Evernote, Bitbucket, Giphy etc. is a real help. It also has apps across all devices/platforms like Windows app, MAC OS, Android and iOS mobile apps, desktop website so its really on the go. It is easy to use, can set profile status, have a lot of emoji's to use and creating a custom emoji is also possible.
Read status of the messages is not available. Apart from that I did not find any drawback while using Slack since a long time.
Just go for it, it really has a lot of features with just one drawback that there is no read status of your message like hangouts, otherwise it is much better.
We are using slack for communication purpose company-wide. Its availability across devices and easy integration with other apps like Google Drive, Jira Cloud, Howdy, Google Calendar, Evernote, Bitbucket, Giphy etc. is a real help.