I managed to pick up Picross 3D at a mall for $20, and I played it for hours and hours. At this point, I've completed nearly 300 puzzles, and now my dad's addicted to it, too. It's a great little game. I don't quite enjoy it as much as REGULAR Picross, but it's still very fun.
I played the demo of it in a Wal-Mart once. It was nice, but I don't think it's complex enough for me to want to buy the whole thing. Maybe if it was DSiWare I'd be more interested.
The game actually gets to be somewhat complex. They add in a couple different kinds of blocks and throw in timed and one-chance challenges, that sort of change how you play the game.
If you can get it for $20 or less then you should definitely go for it, otherwise Mario's Picross is a great alternative.