You might be thinking "what the hell, gridiron and anime!?", Well, you're in for a suprise. I started watching this anime thinking, "hehe this can't be any good" and when the anime fnished, "OH GOD THE HORROR!"
SO! Is you don't know the concept of the story, it's about this wimp named sena who is found by people of the same school, Hiruma and Kurita, while running away from bullies, and these guys find that he has amazing speed and if he trains enough he can turn into this legendary gridiron player. SO! Sena trains and trains like your basic shonen anime gaining new powers every now and then and the way they present is frikkin' epic
The weirdest thing you notice when you start watching Eyeshield 21 is that Hiruma has really pointy ears and Kurita has a head shaped like a slime out of Dragon Quest. DON'T WORRY! You'll most likely get used to it.
Most of the characters are your averagely animated people BUT I rated the animation 9 for the presentation of Sena's (and his rivals/friends) special moves such as the Devil Bat Ghost. It's really epic...really epic.
One other weird thing which I noticed is that EVERY TIME they get a touchdown, get tackled or catch the ball, the helmet always falls off, but I guess you can get used to that as well...
ABSOLUTELY FABULOUS! The character voices are all executed very nicely, but my favourite was Hiruma and his sly voice and his laugh and his "YA-HA!"
I liked the opening and endings but the ones I liked the most were all the ones near the end of the series.
The OST was AWESOME, I loved the music when sena does some tricky awesome thing but then again I guess that happens in most animes.
The characters were pretty much your basic shonen anime characters, which is a good thing. Sena the guy that starts out pretty weak but gains powers constantly, Hiruma the guy that is 100% sure that he'll never lose and always has a plan, then there are your comedy relief characters and more. (I don't know how to do a character section review)
DON'T THINK IT'LL BE BAD JUST 'CAUSE IT'S ABOUT GRIDIRON/AMERICAN FOOTBALL!!! This is a great anime and I loved it, (except for the episodes which I presume are fillers here and there)
(sorry for the long review, first time reviewing, feedback please!!! Oh, yeah, and the series doesn't end where the manga does so I have to buy around the last 7 volumes of the manga, THANKS!!!)