I don't mean it was bad as in outdated processing tech, more that the design was bad in terms of having just one analogue stick, focusing on a gimmick that nobody ended up wanting, and having a worse screen than the PSP that launched 6 years earlier.
The Analogue stick is probably the only thing that REALLY sticks out and was a major design oversight. But that's also not new. The GB needed the GBC to make up for going a bit TOO cheap. The GBA needed the GBA SP to light the screen.
I think functionally the 3DS actually works rather well. Only a few games needed that second stick badly since...well games designed for it were designed usually for single stick play. The screen quality is the more jarring thing for my personal taste. They traded too much there for the 3D. And I actually like the 3D.