It is reported that the Microsoft server currently takes a very serious battering.
Some poeple end up with endlessly frozen downloading attempts for that reason.
I also read that the download from Steam is a loader that downlaods the needed I think ~ 100GB from Micriosioft. However, that main download seems to count as gaming time, so it counts against the Steam limit for game time spent in case somebody wants to refund.
Feedback by those who played already, reports some crashes, quite some report very low frame rates 20-25 even on higher end rigs, but also many overwhelmed customers.
I will join the party, but probably not already this week. Lets see how the birthing issues level out.