One issue is that some puzzles really take a while to think about, which is definitely not a fun thought since a DS is running batteries.
Although the DS Lite has proven to be one of the longest-running portable electronic devices I've ever noticed. I don't even think about battery life any more. Even with my 5G iPod (which supposedly has 16 hours of battery life) I find myself a little self-concious of continuous usage. Where-as, the DS lite feels like it could run forever.
I'm glad to hear this game is so good, I saw a bunch of copies yesterday, and I'll have to pick it up sometime.