Seeing your list of favorite mangas, there are no reasons for you to not like ES21
It has a great story, a very good art (though at the beginning it's isn't that good but it gets really better from volume 05 onwards), a lot of funny moments, also movings parts, and, last but not least, the best characters ever. The fact that this is a sports manga about american football should stop anyone from reading it, because it's unlike any other sports manga ever released, and most of the regulars here in the Eyeshield forum like myself don't even like american football
Even those who likes american football likes it anyway, it just seems that everyone that gives this manga a try ends loving it. I have yet to find someone who doesn't like it after reading it, actually.
So you can go for it. It is part of the best four of Jump (with One Piece, Naruto and Bleach) for a good reason : it's one of the best mangas ever