Episode 15 touched upon the "secret identity" aspect of Eyeshield 21.
While initially a decent running joke, I found Mamori's part in it (the Lois Lane role if you will) to grow tiring rather quickly. It serves as a reasonable counterpoint to characters like Monta and Shin who aren't fooled for an instant. But even then, after the first few iterations, I want them to move on to the football and not "how are we going to fool Mamori this time."
This episode actually felt like it was dragging towards the end right up to the point where Rui kidnapped Mamori. The moment when Hiruma pulls his Sparticus manuever was the turning point and provided the big payoff.
Hiruma remains my favorite character with his unorthodox training methods. It seems like it would be a fine line between manipulation and sadism, but Hiruma manages to stay right on the edge without going over.
Overall, this episode works as it allows them (hopefully) to put the secret identity gag on the back burner for a while and go back to concentrating on putting their team of misfits together.