These dungeons have random layouts each time you visit, with wild Pokémon that attack, various traps and obstacles, items to collect, and a friendly Pokémon in need of rescue. There's a central town hub, which is small but full of endearing Pokémon roaming around or managing one of a handful of important shops, and then there are the dungeons that you visit for the actual quests. The setup is all very typical for the mystery dungeon crawler.
Slightly magical, slightly unsettling, a tiny bit forgettable, and at the same time a tiny bit of it will be burned into your mind's eye. Then there's the fact you are literally a human trapped inside the body of a Pokémon, and that you keep having these rather disturbing dreams, and all the contrast and saturation seems to be dialled-up beyond the natural average, and yes. The pixel art is gone, replaced with a kind of watercolour splash, and as such you're reminded, a bit, of that classic quest in Oblivion (no that's not the game I was thinking of) where you're stuck inside a painting. Mystery Dungeon DX is a remaster of the Pokémon Mystery Dungeon Blue Rescue Team and Red Rescue team games that came out in the early noughties, and one of DX's headline revisions is how it looks.
Much of that dreaminess comes from a fairly obvious source.