Although I've ordered a PAL model from here due to having a large PAL collection already, I have had a chance to play on a Japanese import earlier and as such can offer my views on it for those of you who are undecided.
The 3D is superb. The new IR tracking feature enables you to view the 3D effect from any angle, and it automatically adjusts it so that the 3D effect does not break whilst moving the console. Anyone familar with the original 3DS knows that this is a HUGE improvement to the poor 3D that was available before.
Due to the upgraded specs (four times the amount of RAM), the console is significantly faster. The boot up time for the main menu, suspend screen and game loading is much better than before, with Smash Bros loading in mere seconds.
The other new hardware addition is the C stick. It's not really a stick as such, it's more of a nub like on lenovo thinkpad laptops. It's odd, but works really well once you get used to it – just don't go expecting another stick like the one on the left.
The design of the console is much better this time around too – all of the buttons and ports have been moved from the side of the console to the bottom edge making it far more comfortable to hold. The speakers are also far, far better than the original 3DS XL providing a nice loudness on full volume.
So yes. It's a brilliant upgrade, and is worth getting if only for the near-flawless 3D effect. Also bear in mind that from this point onwards, there will be many games that are enhanced or exclusive to the New Nintendo 3DS such as the upcoming port of the Wii's Xenoblade Chronicles which is confirmed as only working on this new console and not old 3DS models. Majora's Mask 3D is rumoured to be another.
I can't wait until I get my PAL unit next month!