I tried a 3DS out recently at a Best Buy. It's pretty cool. Unfortunately, the only game available to try out was Pilotwings, which was meh for me. I wanted to try the AR stuff out, but they didn't have it available on the demo.
The 3D effect is different than I am used to. Things don't pop out as they do with other forms of 3D entertainment. Rather, the 3DS's visuals create the illusion of depth inward. The real downside of the 3DS right now is its battery-life, which is about 3 hours with the 3D turned on. I hear Nyko is selling a battery pack that attaches to the system, however. So, for the price of making the hardware bulkier (and 20 bucks) you can play for a few more hours.