There was an N+ level pack released today, and fortunately they’re an easier set of levels, as I’d hit a difficulty wall in the standard set of single-player levels. And there are two more packs on the way, also pretty cheap, so it’s a good deal overall.
I also tried out the trial of 1942: Joint Strike, but was rather underwhelmed. You only get to try out a single mission, and it went straight from being relatively bland and easy to a nearly game-ending bullet hell as soon as I reached the first boss. Pass.