I'm leveling pretty slowly at this point. There are probably two dozen folks in my guild that have already hit 60, but I'm still plugging along at level 55 working my way through Maldraxxus.
Part of it is I haven't really invested an excess play time at all into leveling at this point. This is a busy time of year for me IRL, so I'm just squeezing in time when I can. It took me over a week to hit 60 in BfA and it doesn't look like this time is going to be much different.
Couple of learnings so far. I started out by doing most of the side quests in Bastion and now that I'm farther along, it seems pretty clear that was completely unnecessary. Particularly if you're queueing for dungeons as they unlock and getting the xp from them, I'm not sure the side quests are going to be needed at all. The big unknown at this point is whether the achievements related to those side quests will be needed for unlocking flying. With the achievement not currently in the game, there doesn't seem to be any way to tell.
The campaign part of the leveling process feels much more linear than almost anything that Blizzard has ever done before. I personally don't mind that, particularly since you'll have the Threads of Fate leveling option available for later alts. But if you were planning to level 40+ characters to 60 like I might, not being able to mix things up would very likely drive me nuts after a while. The Threads of Fate option should almost completely mitigate that though.
My affliction warlock is feeling pretty strong. No issues at all with completing anything at this point. Also ran the Necrotic Wake dungeon, and that felt pretty decent as well, although none of the gear that dropped ended up being an upgrade, which is a little disappointing.
Professions also feel pretty good at this point. I'm keeping them going while I quest and it's been nice that I actually have useable gear that's available as I'm leveling the professions as well. It's been a LONG LONG time since that has been the case.
So far, I'm feeling pretty positive about Shadowlands, at least in terms of the initial leveling process.