GG could have been more menacing but he was far more memorable than Loki or Red Skull. Also, when GG died it left an impact on the protagonist and the audience (especially with how Harry took it). Peter's victory over Norman felt sad, but poignant. I remember thinking when Red Skull was defeated, "That's it?"
To put it another way, what left more of an impact when it was over? Peter's guilt giving way to Spidey's joyous final swing through the city or Cap in Times Square muttering, "I had a date?"
I'm not picking on Cap, but I honestly think that after the summer 2011 Cap and Thor will lose their newness. I seriously doubt we'll be talking about them in ten years the way we talked about SM1. Call me skeptical.