I don't mind it, especially when I'm sitting on the can and have nothing better to do, better not the best controls than no controls, but I have to admit, I prefer even the Wii U Gamepad over the 3DS, mostly because I like having the second stick as a way to guarantee smashes so I won't accidentally tilt instead. it doesn't help that after going back to the 3ds when I originally got the Wii U Sm4sh and used the pad, it felt like I was playing Super Smash Brothers For Ants.
Also, how can anybody play on the 3ds at all without one of those ergonomic controller backings? I have one and even if it's not as portable, it feels much better in terms of grip.