Same. Although it got significantly easier the more times I played it. The first time took like 2 hours. Later it was about 30 min. I think the devil walker was the hardest part because the splash damage from that giant gun is ridiculous. There were so many times I was behind cover thinking I was safe but if that gun shoots anywhere near you you're dead.

Same here. The boss would come out and I would get literally covered with various Hive/Fallen creatures of different levels. And they were no longer easy pushovers. Once the boss appeared, all Fallen enemy seemed to charge up and gained shields that they don't normally have. They also became much more aggressive and tried to corner me so that I could not get good access to the boss. I didn't notice this one the first day I played, but by the 3rd/4th day, it was happening every time. I thought it was because I was leveled up more, so they became more difficult/aggressive.