A continuation of a series that is past its prime. With the ability to import people, places, and things from the original game, it literally steals from its past. This series will not move forward until it stops looking back.
In fact, for casual Warriors players, it may even be better to have not played the first game, as the main game probably will make you less likely to want to play the new, but not all that different, content.
Assuming you have dipped your feet in the pool of endless Dynasty Warriors content, it's almost absurd at this point to have to pay 30 bucks for either the PS2 or Xbox 360 flavor of what is barely more than preconceived, half-assed, tacked-on downloadable content.