In a word, cruel. By the halfway point every other cave sublevel comes with enemies that'll horribly maim you and your army in new and creative ways. And somehow I still like it. The fundamentals of Pikmin are still here and dungeon-crawling adds some meat on top of the time-management and puzzle-solving in the overworld. As annoying as it can be, I find the combat pretty engaging and it feels good to beat tough enemies once you learn their vulnerabilities. It can be a very fun game; just be prepared to sink in a lot of time if you need to reset levels a lot in caves.