I love how much content you're producing, and I was thinking about how at times I really wanted one of your level themes, but it wasn't the right vibe for what I needed, so I thought of something (that you may already be doing?) you could combine different terms together to keep generating new kinds of backgrounds, so "theme" and "atmosphere" for example. Theme is forest, snow, lava, countryside etc. and atmosphere is sunny/happy, gloomy, creepy, haunting, whimsical, etc. and then you can go through the combinations, eg. happy forest, haunting forest, etc. and someone is sure to find something they like!