I upgraded a few weeks ago myself. Needing to unscrew the back panel to get to the microSD card slot was annoying, not to mention having to buy a microSD card to begin with. Why didn't it just use SD as well? And it's harder to sell your old 3DS because the N3DS doesn't come with a charger, so you have to explain that to the person you're selling to. They either have to buy their own, or you give them one and go buy one yourself. I have yet to play a dual-analog game (even though I own Kid Icarus and Monster Hunter 4), but man, that second circle pad sure is stiff. I hope it works as well as I thought it would. At least the battery is far, far better than on the OG 3DS. Now I don't have to charge it every half hour.
Overall, I give it a C. Great if you don't have one already, but probably not worth it if you do or don't have any games that would benefit from it.