So yeah, the 3DS is pretty cool. 3D without glasses is a gimmick that actually works pretty well, at least by gimmick standards. It's just a shame for that part of the population who get nausea or headaches or other symptoms from it.
So the first thing I noticed was that the higher the 3D slider is, the more tetchy the 3DS seems to be about you looking at it from exactly the right angle. At first this meant I had to leave it on about half-3D, but I soon grew accustomed to the habit of getting the right viewing angle, and can already (I've only been playing it for about a day and a half) generally go straight into full 3D without much trouble.