Increased cabin pressure increases humidity, which in turn results in (for me at least) a reduction in issues like dry eyes, dry skin, and sinus problems. In addition, the increased oxygen is extremely noticeable - when you get off the plane you feel more like a human being, even if you've only got 4 hours sleep.

Note that my experience in comparing the A380 to the 787 is on USA - AUS flights, so your mileage may vary on shorter flights, but on longer flights it's a godsend.

E: I also have way fewer issues with my stomach/gut on the 787.