I found this Anime simply, amazing. Instead of having short series Anime's who compacts everything into 12 episodes, Eyeshield 21 gives you the full development of the character itself.
The Anime follows a short and weak gofer, Sena. Throughout his life he has only ran errands for bullies and has always been protected from someone he considers his older sister. Sena had never done anything for himself; until he discovered something he loved, Football. As the Anime goes on, you will see Sena develop not only as an Ace Runningback, but as a person.