I'm closing in on the completion of E3M5, but that's not the only thing I've been working on all this time. I've gone through all the previous levels a bit to touch up any errors and make small adjustments.
The biggest feature I added were tomes that bring up messages when you collect them. There are several in each level, and they have special messages that reveal secrets, story elements, and sometimes nothing more than offhand cultist comments. They're not always right in your path, but if Caleb gets curious and starts searching every corner he should be able to find them all.
They aren't essential to actually conquering any of the locations but I thought it would be a nice feature for those who take the time to wander around each map looking for goodies.