i just finished this one and i was LOVING it (love me some tsundere chicks!). Unfortunately they REALLY lost the plot with the last few episodes. And boy what a terribly done ending. I wish more writers would end their shows in a way thats actually fitting, instead of going for cheap shock value followed by massive deus ex machina so they can go "oh nvm!"
seriously its a trend that ruined like a billions shows for me. But anyway. H2O is WELL worth your time if you're used to how bad 90% of anime endings are. Its a really good show and I was really crushing hard on Kohinata ^_^