I'm sure it will be playable and probably worth running through completely, but I ain't expecting greatness. Looks like they're using the BiA DS engine, and let's face it, Ubisoft gets the job done on DS -- nothing more.
I still think Rockstar made the right choice, though, with their approach. They were able to offer a complete GTA experience on DS because of how things stream in. You can already see what appears to be a much more barren city in COP, and again, though I think it will likely be a decent romp, it likely won't hold a thin birthday candle to Chinatown Wars. Glad they went with a behind-the-back view, as it will be cool to have a game like that to play on DS, but I wouldn't get my hopes up, folks.