The new device's two 4.2" screens are reportedly "93% bigger" than the screens on the Nintendo DS Lite and provide a wider viewing angle. The DSi XL also features an improved "pen-like" stylus. The device will initially be available in dark brown and wine red hues. In addition to all of the functionality of the Nintendo DSi, the new handhelds will also come pre-loaded with Dr Kawashima's: Little Bit of Brain Training: Arts Edition and Dictionary 6 in 1 with Camera Function.
Based on the photographic comparison, it would seem that the larger screen size of the DSi XL affords a significant improvement over its comparatively minuscule DS sibling.
I've never been much of a handheld gamer myself but the new model is intriguing enough that I'll likely check it out when it makes it's way to North America, which Nintendo says will be some time in the first quarter of this year.