Things I like:
-more space underneath the Plus pad
-matte border around the top screen... and everywhere! Shiny is nice, but slippery and fingerprints easily.
-actual Select, Home, and Start buttons
-rounded edges means no corners digging into your hand during certain games
Things I'm unsure of:
-shape of the LEDs. *shrug* I'm used to my 3DS's square ones
-recessed text on the buttons and other locations on the system provide spots for grime to get stuck
Things I'm pretty sure I wouldn't like:
-if it's anything like the DSi XL, it'll be heavy. Not ideal for stylus games where you're holding the system with one hand
-on top of that, due to the larger screen, it'll be further from your face. Holding a heavier system further from you just makes your arms more tired
-not as travel-sized
I'll mention it to my mother - she loves her DSi XL, and didn't want to downgrade to the smaller 3DS screen. There's a pretty good chance she'll want Professor Layton and the Mask of Miracle, which might motivate her to buy the system. I don't know if she'll bother, though. At this point, she doesn't play that many games, other than really casual ones on her iDevice.