Atlus sent word today that Etrian Odyssey Untold: The Millennium Girl is out now both at retail (with a fancy CD and art book) and digitally via Nintendo eShop. Untold gives Etrian fans a story mode for the first time, so if you've been curious now's a good time to jump in. I'm not very well-versed in EO, but I can say it's weirdly fun to draw dungeon maps while you're exploring.
My 3DS XL is completely overflowing with Atlus games, but why isn't yours? I've been using the eShop quite a bit but Atlus's second bit of news still applies to both retail and download. You can get Shin Megami Tensei IV for $10 less at October 14th. I'd say it's scary how good this deal is, but I'm afraid Atlus isn't cooperating with that one.
Bottom line, if you like the RPG genre or can get into the narratives you'll see dozens of hours fly by.