It's not a successor so much as an upgrade of sorts (think «Nintendo DSi to Nintendo DS», rather than «Nintendo 3DS to Nintendo DS»), with just a bit more power, a right -
hand analog nub, and a few other features.
The biggest change is the addition of a second
analog stick on the right
hand side of the console: a small
nub absent on earlier devices unless you owned the CirclePad Pro peripheral.