There are a few nitpicks, but the brighter, stunning screens make me forget about them most of the time. Games look totally different - colors I had never seen before, like the yellow/gold chains that hold the lamps up the Haunted Mansion part of Mario Kart. The backgrounds of some games which I hadn't even noticed before because they were so muddy jump out like I've never seen them before.
That said :
1) I prefer a power button that clicks or is switched, not a slider; I see no need for it, and it feels like it may wear out.
2) The start/select buttons were better where they were; you could hit it quickly in a game (say, Mario Kart) to pause without screwing your game up, now it takes that extra split second to hit the button and I can never remember which one is which.
3) The volume is much lower than on the DS Phat. The speakers are nice and clear, just sounds about 1/2 as loud as the other model. No issues with the slider or anything, it just is terribly quiet when compared. I'm sure this was to reduce annoyance to other people, but when I'm playing my DS in my house alone I want it LOUD.
Other than that, I love all the changes. I like the d-pad now, makes turbo-boosing in Mario Kart and other moves that require d-pad dexterity easier. The shoulder buttons are more friendly.
The fingerprint thing is an issue, but the Polar Whites are the best in terms of hiding them. I was dead jealous about the Black DS Lites until I got my hands on one of the navy blue Japan releases, and I'm glad we got the white in the U.S. I'd be wiping fingerprints all day off of the black, but they only show up to the eye in most lights on the Polar White when they are really bad.
Best upgrade I ever made, and the only regret I have is that the original DS had such muddy, dull screens that I played on for so long.
SPP