I posted quick thing on my facebook about it but just thought I would throw it on here for anyone in the market.
My son has a DSi and he wanted to play mario kart 7 sometime... well found out it was only for 3DS so he sold a bunch of his old toys to buy a 3DS, which I wasn't so sure about, thinking it wouldn't add much of anything other then new games... but boy was I wrong.
The thing is pretty amazing. It can take 3D pictures and videos (video in firmware update on the 8th). You can now make "Miis" for all your family and friends plus it will set up the face based on a picture you take. It has a couple games/silly things to take a picture of your face in 3D and then shoot it and make it talk. The 3D part can be turned off too turning anything into a 2d version without any major loss in quality. We got the pack that came with Mario 3D, not only to save money but gave him a game to play right out of the box.
So anyways, he had been playing all day on/off and I thought it looked pretty cool and then he wanted me to play. I didn't put the shit down for like an hour... thought it was like 10 minutes. It is definitely 3D in nature but still has a nice 2D feel to it. Closer to old school Mario than the Galaxy series. They have a sort of mix and match from all the Mario games. There is a takooni (i think it is spelled) suit that has a tail and can float, a box with a propeller on the top to act much like the orange suit from New Super Mario on the Wii. Typical fire power and probably a lot more. I am only on world 3 right now but I saw my son in a turtle dude suit that shot boomerangs. Three star coins per level (like super mario on SNES) and they are used to unlock levels and items/etc as you play through the game. New switches can be activated by tail swiping things to raise platforms and such. The brought in the cannon and looking around like in Mario 64 in some levels. The cannon and binoculars are used by activating the gyro in the 3DS so you move the console around to control it's aim... pretty intuitive to use. At one point in one of the levels it brings you back into Mario Bros (NES) level design and final flag/castle.
Just an overall amazing experiance for me and my son loves it. I have tried using the 3D but it has to be held like 10-12 inches from your face to work well and I didn't feel comfortable doing it... so the whole time I turned off 3D (which is simply done with a slider on the side of the screen) and I have had 0 problems that I thought 3D would be necessary.
I also use an acekard2i which doesn't work right now (since I upgraded to the latest firmware) but they are in the works on fixing it. DSTWO cards work on the latest firmware so it will be possible. Also 3DS roms don't work on any card as of now... but again should work down the road.
Just my two cents