I finally got a 3DS XL last week and I'm still trying to figure out how it works. I was content with my DSi and all the games I have for it, but Pokemon X/Y was the main reason I decided to upgrade and I have to say, I am really impressed with it and it was money well spent.
First thing I did was transfer all my DSiware games to the 3DS.
Then I ordered several games:
Animal Crossing New Leaf
Monster Hunter 3
Harvest Moon: Tale of Two Towns
Harvest Moon: A New beginning
Heroes of Ruin
Resident Evil: Revelations
I also purchased 3 $50 credit cards ($150) for the eshop that I plan to spend soon cause I managed to amass a rather large wishlist.