Knowing GOG Galaxy has built in multiplayer & matchmaking. Does Diablo use that or it still uses the old battle.net service? I was just curious because I stumbled apon Diablo on GOG but never actualy played Diablo (played Path of Exile...sometimes).
from what I understand, there's 0 connection between multiplayer in gog's diablo 1 and GOG galaxy.
They've just been given a copy of d1's bnet to run. (it's exactly as clunky as the original)
If you want a quality multiplayer experience, https://github.com/diasurgical/devilutionX
is something to look at.
Latest beta version adds zerotier support, which lets you play multiplayer without forwarding any ports.
After we add a game list, playing with random strangers will be really one click away :)