Mine would be either Assassin's Creed or Onimusha.

Assassin's Creed is something new (at the time) and has kept on growing and it is definitely the best new series of the last 10 years.

Onimusha is an awesome series. I absolutely LOVED Onimusha 3, and am disappointed that the series hasn't kept going. Hopefully it's something Capcom can look into bringing back soon.

Also, I didn't know there was so much love for Onimusha.