I think if you were a fan of King of Fighters when younger, definitely go and buy this. It should be right down your street. But for anyone who is unfamiliar with this series, I would only advise you to buy if you can find at a good price, as there is many other games more worthy than King of Fighters Extreme.
As a game to get excited about, Call of Duty fails spectacularly. What we have is an exercise in frustration, and not something All About N-Gage can recommend. Some people may enjoy it, but they'll be few and far between.
If you're looking for something to play for 5 minutes on the bus, then this might not be for you. But if you're wondering how to pass time while having to sit in a car or a train for 10 hours (and a boring conference plus the trip back), then Shadowkey is something not to miss.