It's more comfortable to hold, the circle pad is smoother and has a more rounded edge, and the screen is huge. If you like those things, then it's worth it.
The resolution is the same as the original model, so the new screen is pixelated and very noticeable. Once you get over that fact, it's no big deal. I hated the first model because it was too small and cramped my hands.
The one con I know will definitely come as a disappointment is the audio quality of the speakers. They made the molding of the top half thinner, so they had to use smaller speakers... and they lowered the overall volume to try and mask the loss in quality, but if you try to play a game on full blast, you will want to plug in headphones.
Bottom line: Worth it