This game is absolutely brilliant! If you are a fan of the Dynasty Warriors or Samurai Warriors series, then you simply must buy this game - nearly 130 playable characters (including guest appearances from Ninja Gaiden/DOA characters Ryu and Ayane), with plenty of stages, weapons and costumes to unlock - this game will keep you busy for months.
For those of you that don't know, you select a team of 3 characters and take them onto the battlefield to defeat thousands of enemies in each stage, along with other objectives. The story follows an interesting concept of travelling back in time to save your fallen allies, so that you can slay the Hydra Dragon. The story can last as long as you want it to - you can try to take on the Hydra straight away, or fight the other battles (around 30) to rescue your fallen/missing allies - which is probably the way you will get the most out of the game, and to get every character could last a good 50 hours or more. Co-op is available both online and offline and is great fun (especially offline). The Japanese only voice work may not be to everyone's taste, but personally it didn't effect my enjoyment of the game.
As I said previously if you have enjoyed Dynasty/Samurai warriors games then this game will be great for you, as it incorporates a the best bits (and all the characters) from both series. If you are new to the Warriors franchise and love action/adventure/fighting games, then I would still highly recommend this game!