Honestly the only time I REALLY noticed it, was at a store display where they had a regular 3DS and the XL right next to each other. While the larger screen is a little more pixelated, it's not bad.
What the bigger screen does get you is a lot better 3D effects. I can barely see the 3D effect on the normal sized screen, and it makes my head hurt after a few minutes. On the XL, the larger screen accommodates the 3D effects much better, and I can play for quite a long time with no issues.