Etrian Odyssey is an old-school RPG in the vein of Wizardy or The Bard's Tale. That is, you assemble a party of adventurers, go to a town hub to gather quests and equipment, then delve into an uncharted labyrinth killing monsters and mapping your progress. There isn't much of a story to follow here. Your goal is to find the "secret of the labyrinth" which, spoiler alert, has something to do with global warming (97% of scientists agree this is a dumb twist). Exploration and combat are the real core of the game, and the mapping of the maze is the primary gimmick. A task for which the DS is excellently suited. No need for graph paper. Just use the stylus and mark your map directly in the game. I can't tell you how frustrating it was playing Bard's Tale, carefully mapping away, only to have my time-consuming efforts foiled when the map ran off the edge of the graph paper. I'd then have to tape a second piece to the side or, worse, start over from scratch.
I'm sure there a lot of players who would still be turned off by the thought of not having an auto-map feature, but I find it oddly rewarding. In a way it gives the game a casual feel, almost like completing a Picross puzzle. This is despite the hard-as-nails difficultly of the actual game-play. The game is relentless in throwing random encounters at you. Many of the spells and power-ups try to address this by temporarily lowering the chance of battles. But these random fights are pretty much par for the course in Japanese role-playing games and which is why I typically try to avoid JRPGs (Phantasy Star being another exception). However, in this instance they are the core of the experience. Never fear, there is a gentle progression as your characters gather experience and skills. In each case as I worked my way through a new level's difficult monsters, by the time I reached the next stratum (the labyrinth's sections), I was easily steam rolling over the those same monsters who were troubling me a few floors earlier. Mindless, yes... but, even with the general lack of narrative, also weirdly satisfying.