This is a MUST READ (if not the BEST) sports manga, even though you might have no idea what American Foorball is. The best things I like about Eyeshield 21 is Characters' Development, which I give a 10/10:

Most sports manga have characters who are gifted or simply acquire some 'special traits' that make them suitable: Sawamura, Kuroko, Hanamichi,... Eyeshield 21 brings up a game where even the weekest player, or someone without any talent, can become the star. Not to mention, every character in the series have a lot of chances to shine and development.

Because the nature of American Football, where a team requires players specializing in one field (Speed, power, technique, catching, tactics, etc.), and there are a lot of one-on-one situations happening on the field, no character is neglected, and the intensity of the series come with, two words, tactics. Like One Outs, the author builds the best character of all time (in my opinion), Hiruma Yoichi, who overcome any hardship and CLUTCH situations using trick plays. Hiruma Yoichi is one hell of a genius, in comparison with great mind like L , Light and Lelouch. However, the fun thing is that his tactical plays come from hardcore practice, which bring the whole team together.

Story: 9.5/10 - The action throughout the game is every intense, while the tournament bracket is full of surprise. The author sets up for the team, SPOILER ALERT, to lose early at the very first game, so that the team can go training early and ready for their final tournament. So, yes, you will not be let down from cliffhangers like in Diamond no Ace. The plot twist in the manga is real, and it occurs very unexpectedly (according to all the comments I read). And the manga gave you goosebumps on every one-on-one situation.

Drama/Romace: 9/10 - There is actual drama/ romance relationships between a few characters in the manga. And they are very satisfying (Definitely better than Nise Koi).

Art: 10/10 - This comes from the artist of One Punch Man. So if you saw OPM first, you would see some characters with similar designs (Not Saitama, though).

Sportslike? - at least 9/10 - Of course, it is manga. So it is understandable that Japanese high school players can be a little bit overpowered. However, it is actually not at the level of UNREAL actions like PRINCE OF TENNIS. Many of the actions in the series are actually seen in many NFL games, though not usually. The timing where the new skills come up in the game definitely make you scream like any sports fan. My enjoyment with this manga makes me re-read it at least 5 times.

Comedy - 9/10 - If you feel OPM funny, then the comedy in this series is around that level.

SPOILERS ALERT - My disappointment is that Hiruma Yoichi is not annouced MVP. However, the game vs. American showed us his worth. And rumors said that Hiruma Yoichi is actually the MVP of that game and given the opportunity to play football in US, but he gives it to Sena in the end.