Oh God, where to start? There are a lot of things wrong with Battlegrounds functionally with stupid interactions and bugs. However, I think the biggest issue right now is the game design is incredibly flawed. You'll have to bear with me as I try to explain something that isn't that clear in my own head.
First the inconsistency between tier power levels. It feels like tier 2, 4, and 6 are far worse than 1, 3, and 5 and there is a desire to skip them when possible. Getting to 6 feels like an option especially given that the cards on tier 6 aren't good enough to justify it. Unless Amalgodon of course.
Second the inconsistency between the number of minions per tier. It is fine that there are more copies of lower tier cards, but I'd like there to be the same number of minions per tier. For example, if there are 12 possible tier 1 minions, there should be 12 possible tier 2 minions, and so on. I also think the types of minions should be evenly distributed too. 3 of each type (including neutral) on every tier for example.
Finally, the insane amount of damage taken. Sure, there is a damage cap but not if someone concedes (me a lot lately lol) or disconnects. Sure, it makes for a less dragged out experience, but it kills the end game possibilities most of the time and doesn't incentivize going to 6. It pushes it more towards midrange and letting tier 1 units run the show.
These are just the main ones for me. In my opinion, the designers for this mode are likely inexperienced and there is not nearly enough people working on it to provide the needed feedback. I'd prefer consistency and concrete design ideas rather than throwing shit at the wall and seeing what sticks.
Not sure what bugs make it unplayable. I certainly am not seeing anything game breaking and have no disconnects. I think the Khadgar/Baron pirate interactions are stupid and buggy, but not game breaking.
I'm pretty happy with the game right now especially since late game builds shine without Diablo around to fuck everything up.
The single thing that is wrong with battlegrounds is the electronic roulette algorithm that drives it.
Who goes first, who you play against next, whether you get a triple, what minion gets hit and in what order… the list is endless and the entire thing is controlled by software.
There’s nothing that the player can do. No strategy can mitigate any of the above as it’s all controlled by software.
Who goes first is only random if you have the same amount of minions. Attack order is left to right. There are various ways to manipulate what minions get hit and when. There are plenty of times where who you play is not random. I'm not sure you actually play the game.
I think the game is actually quite good right now with armor and the removal of Diablo. No complaints on my side.
Also, Elementals are not suddenly OP. They just have more time than before to actually scale. Dragons and Murlocs also benefit greatly from this.