At first, I saw the dsi as a mere gimmick, with a bigger price tag. In a sense, it's true. I thought the camera would be useless, the screens would look ugly, since they increased the size of the screens, it had less battery life, and so on.
Not too long ago, I actually got to play around with it, and I was pleasently surprised at it. The screens are obviously bigger, yet the screen didn't look awful, even though it was again, bigger than before. The camera, was obviously bad, but for such a small screen, it didn't look horrendous. Just.... never take it out of the DSi, otherwise, it'll look awful. I didn't get to try out the other functions of the camera, like disorting the shapes of people's faces and such.
Surprisingly, the D-pad, was improved as well. It felt like the hybrid of the DS Phat and the DSL's. It looks the same as the DSL's, but it felt much better than my current DSL. The L and R button were redesigned, so it felt more natural to my hands. I always found the DSL's D-pad awkward, so it was a nice plus.
My only disappointment is that the battery is shorter than before. But since my DSL only lasts around 6 hours on minimum brightness settings, I don't really mind it (2 years old.)
In conclusion, I liked it quite a bit. Improved D-pad, bigger screens, cameras, and a few multimedia functions. Are the upgrades worth the extra cash? In my opinion, no it is not. Many people will disagree with me, and it's perfectly understandable why some people like it so much. However, with it being over 200 dollars, (In canada) I'd rather wait for the prices to come down a bit. Other than the price and the battery, I really have no major complaints. I think it's a good upgrade over the DSL.