The release date for Etrian Mystery Dungeon has been confirmed by NIS America to be September 11 for Europe. The North American release is still not known but it will be dealt with a separate publisher, Atlas U.S.A.
Etrian Mystery Dungeon will be released as both a physical and digital Nintendo 3DS title once it launches. Unfortunately NIS America hasn't mentioned the install size, but it shouldn't be too large.
Etrian Mystery Dungeon will be an RPG title with turn based combat that incorporates some unique gameplay features. Choosing the right abilities and skills will be important as you'd expect, but the strategic positioning of your party also plays a large part in your success.
From what we've seen so far, this new combat system looks like it could be incredibly engaging, and I personally can't wait to see how it plays out in real time. Mystery Dungeon will have a number of different classes that Etrian Odyssey fans may be familiar with. Classes such as Landsknecht and Runemaster will be in Mystery Dungeon. Players will also have greater control over customizing the individuals in their party, and the game will feature a bunch of Etrian Odyssey style skill trees.
The dungeons in Mystery Dungeon will also be procedurally generated - no two dungeons will be the same, and I think this is a great route for NIS America to take. As you continue to play, the dungeons will start to become more challenging, alongside the monsters you'll have to fight.