The reviews are quite polarising no? I imagine this game would have hit the upper 80s if it got the technical issues right.
Personally I think it will sell well regardless of opinions, Mass Effect has that kind of draw. If Bioware are smart they will get to updating and addressing these issues immediately and put out some awesome DLC for later this year. Much like Witcher 3 did, that had many new animations added, a UI overhaul and many more.
I think another thing to consider here is that the team that worked on this is pretty much new to this franchise.
I'd like to believe it's the technical​ issues, but the key point for me is that reviewers typically praise BW story and characters almost universally as a plus, whereas here the reaction to that aspect is mixed at best. That's pretty worrying to me, since BW could fuck up everything in a game and I'd still.love it because of their character writing (coughDA2cough).