PS3 is a considered a failure by some because it didn't make Sony any money but instead lost them tons. It had a turnaround in fortunes but overall its main success was in keeping the Playstation brand relevant and cutting the losses significantly which put Sony in a good position to launch the PS4. In that sense it can be considered a small, yet significant kind of success. My point basically is that success isn't necessarily a binary situation where "greater than" or "less than" sales are the sole determining factors. I'm not saying the 3DS is a success...yet, but being behind the DS doesn't automatically disqualify it.
It also missing all Nintendo forecast until now. Something is not going well, clearly.