Portability (size / weight)
This is my favorite toy. The battery lasts forever (15 hours or so?) and I love that you can just plug it in to recharge. There are so many games out there for this...you just have to hunt them down as many are obscure or only sold in certain places. Also, you can play games from around the world on this thing...no region restrictions. Touch screen interaction is very cool and works quite well. All in all it's a brilliant design. I also love that there are many games out there for this that are not your standard shooter/action games...like Picross, NYTimes crossword, etc.