Having played a few AOW4 maps, I gotta agree with the underground being a lot less interesting to play with/against in this iteration than it's ever been in this series.
It's also pretty bad visually. While some effects are decent in isolation, like the lava, the placement doesn't make sense (I saw water right next to lava on at least 2-3 maps, you'd at least expect some obsidian where they touch) and the overall visual variety is lacking. In fact barren areas where the same tile repeat are rather common. There's also an overdone reddish fog and it's too dark to see the outline of what you've explored properly... I keep zooming out to the paper map to be able to see shit.
The underground generation also creates a lot of roads to nowhere. My scout followed an underground river for ~14 turns, and all it did was snake around a giant lava pool and then dead-end. No resources nodes or anything along the way. Major letdown. Exploration down there should be limited and more dangerous, but the rewards need to balance it as well. Underground should be full of interesting nodes with hidden, resource-rich areas/caches, hidden behind stronger than usual groups of monsters and mysterious wonders.
There's also minimal tile detail compared to AOW2/SM.
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