The only thing that took me some time to adjust to was how overwhelming joining a new server can be. So many channels! Everything needs my attention! But after using it for a long time, I think this is actually a feature. I can mute channels and categories I’m uninterested in, but how many channels on Slack are never found due to poor discoverability?
We run both Slack and Discord at my work and the engineers vastly prefer Discord, for what it’s worth.