This is a wonderful map Raiko - congratulations.

I love your background and cave walls just the way they are: elegant and easy to read. I'm glad you didn't try to make them realistic.

I agree you achieved the 'unified look', and I know what you mean about the collapsed areas. Is the rubble a bit brighter than it needs to be? One idea to get a less repetitive rubble is to find a photo of gravel or similar, stretch it across the entire map so the size of the gravel is about the size of your rubble (you need a really good photo of gravel for this), recolour as necessary, then use a layer mask to only show the gravel in collapsed areas. I've used this technique well in the past (for a dwarf mines map I did). The trick is to find or take a really good photo. I'm not sure how the technique would translate to vector-based programmes.