How did you handle the fight at the end of Act 1?

For most of act 1, fights felt reasonably difficult. There were only a few points where I had a tpk. However, between early access and now, that last fight felt like a sharp spike in difficulty.

My first time through, it took me and my wife 2 days to finally cheese it. This time around it still took us 3 or 4 reloads and something I'll talk about in the spoiler section before we made it.

It seems like you suddenly need to get good at really strategizing or find some extra wrinkle to make it possible. But I'm curious to hear how other folks managed to get through the fight.