H2 and Water Boys are both about high school sport teams (baseball and synchronized swimming).
In the beginning the clubs aren't very popular, but they aim to win big competitions. As they try to achieve this goal, the teammates recognize how important friendship is.
The dramas also share a small town atmosphere and a great deal of characterization, even of the side characters (especially the families of the main characters).
I really recommend these dramas to those who need a break from the current and fast dramas, which often seem a little bit shallow to me.