IIRC the game has framerate issues on non-New 3DS'.
Other than that I don't know much about it.

Sounds like it's pretty much unplayable on non new 3ds systems. (framerate)

Well, 2DS is like a normal 3DS when it comes to hardware and there are some comparison videos on youtube (and 3D don't work on old 3DS anyway). As for the second circle pad, I'm curious myself. :P

I'll probably grab the Wii U version when I get the console. Thanks for the info!

Without a second circle-pad, controlling the camera is going to be a chore. As for the game itself, it is 3/4ths Dynasty Warriors and 1/4 Legend of Zelda. If, like me, you haven't played many "Warriors" games, it is quite fun. The addition of boss battles and using your tools to exploit their weaknesses is pulled straight out of Zelda games such as "Ocarina of Time".

The major benefit of the 3DS version, in comparison to the Wii U version, is the ability to switch between characters on the field. On Wii U, you are locked to one character and have to run yourself ragged racing around the battlefield to complete objectives and/or to help your dopey AI-controlled allies. Being able to just switch control to a character who is being overwhelmed is so much better than having to race to their aid, especially since I never seem to make it in time anyway.

The game is crammed with content and unlockables in addition to the new characters added to the 3DS release. There is also going to be DLC released over the course of the year to add more characters, more costumes and new scenarios. You can purchase this content separately or as part of a season pass.

Please note: I am playing the game on a New 3DS, so I haven't personally experienced frame rate issues.