Larian’s Swen Vincke posted a tweet yesterday showing the game hitting 500,000 concurrent players, making it the third most played game on all of Steam He said that he told IT to only expect 100,000 concurrents at max.
Me and 3 friends have had a lot of fun with Divinity Original Sin 2 multiplayer. There's usually a lot of shenanigans and fun happenings as a direct effect of having several players bringing their own style to the game.
Just be advised that the experience will not be the same as playing single player. From what I understand the multiplayer experience in BG3 is much improved but I found that when playing with friends in DOS2 that I could not for instance take the time to dive in deep with conversations, quests, lore etc as I would like.
There is also a current issue in that if someone joins your game with a custom character, that character will from then on be a permanent member of the party. You cannot at the moment get rid of them in any way.
Bottom line it is fun, but you should treat it as a separate thing from single player - and definately have a dedicated playthrough for multiplayer.
I found that when playing with friends in DOS2 that I could not for instance take the time to dive in deep with conversations, quests, lore etc as I would like.
This is also my experience. IMHO BG3 is also more focused on conversations than Divinity 1 and 2 or at least you can focus more on it. You can also just kill everybody of course. For now at least I feel like only a small part of my time with BG3 was in combat. Most of it was exploring and talking to people. I'm sure coop is fun, but I'd rather play is solo.
I spent some time playing 4p at the weekend. Personally, I loved it. It definitely had the feel of a ttrpg session. Your experience will completely come down to who you are playing with
Just be aware that a lot of the abilities are very different than how they work in 5e and a lot of the descriptions of abilities still need a lot of polishing. I've only tried single player but that's my only gripe.