First, I want to say I like the game at its core, and with a few fixes it will go from good to great!
But, I played online with a friend on the PS4 today, and the lag made the co-op experience almost unplayable. We played as multiple combinations of the characters. We would lag on each other's screens, the enemies would lag, and our attack commands wouldn't be processed. We both have excellent internet connections, so we know the issue wasn't from our end. I've heard similar complaints from almost everyone who's played.
Please fix these lag issues! I know a lot of hard work went into making this game, and I want to see it shine (especially as a long time fan of D&D and Icewind Dale). I love the loot system, combat, narrative, etc. But without a fix for the online co-op issues, it won't be worth it.