So, I've run into a few problems with the headtracking for the New 3DS XL: 1. If I look away (say, to sneeze, or talk to someone) when I look back the 3D is completed messed up and it's a bit jarring. This is a minor annoyance, especially given that I just have to wait for the system to readjust to where I'm looking. 2. The other night while playing MH4U, the face tracker went nuts, and every 5 seconds or so the 3D would go bonkers before returning to normal. I turned the system off and once I rebooted the issue was resolved, but man oh man that was a headache. It's starting to seem like the face tracking technology may be a bad thing. I never had much trouble with "sweet spots" on the old 3DS systems.
Still waiting on new 3DS, the first run may have bugs like shifty auto-3D tracking. I'll wait for firmware updates that may fix it, and most importantly, an exclusive game for new model that I must get before I replace my current 3DS.