The screen and camera are improved. In the internal side things have also received an upgrade for a faster system and better graphics. There have been 'bumpers' added and anot her analog stick, presumably for camera control.
There are supposedly games that will be exclusive to this 3DS/3DXL set. Which it better. At 160/180, people would need a real reason to abandon the current system. I can't say for sure Nintendo has given them that reason. I can't say I'll be running out for one. I will wait to see the exclusives. Xenoblade Chronicles is a good start.