Quite enjoyable.
Pros:
Simple yet engaging gameplay
Great graphics and sound, voice acting is solid
Creating your own combos using the Freestyle scroll is great fun
Nice martial arts drama in the story
Loading times are not long at all
Portable-friendly; you can save the game virtually any time
Cons:
Not very challenging (so far) - I make mincemeat of legions of five or six foes with a few taps of the circle button
Some camera control would have been nice
Movement controls are fast but feel somewhat loose
Chi attacks are extremely overpowered to the point of being nearly game-breaking - the player is only limited by having to charge them up which only takes a few seconds, and they're strong enough to annihilate anything effortlessly
Some more combat options, like perhaps using a shoulder button for blocking instead of for items, would have been nice too
World map is unreliable (upside down maybe) - I spent a great amount of time following the map looking for Western Byakko only to find that I was actually going in the opposite direction
Overall: I enjoy playing this game. None of my listed cons are bad enough to ruin the experience. The only one that comes close is the chi attack thing, but while they are easy to abuse (and the game encourages frequent use of Chi attacks because that's how they get stronger), I never felt like I needed to abuse them. It's much more fun using the varied sword moves (and "varied" is the understatement of the year--there are hundreds of moves in the game) and throwing a chi attack every now and then when you just want to get rid of some pesky archers or something.
I don't know about the game's length because I haven't beaten it yet, but Gamespot says 15 hours, and that's a good amount of time for a handheld action game. I got it relatively cheap and I don't think it would be a waste of money for what you get. Kingdom of Paradise is a great example of how to make a handheld game with console power.