As others have speculated, this version of Molten Man is more of a combination of the original Mark Raxton character and Betty Brant's brother, Bennet, and the result is a more developed a tragic character who is caught up in the downward spiral of being a villain even though he had no intention of ever being one. In some ways, though, this version of Molten Man reminds me a bit too much of the show's version of Electro, as both characters are essentially victims of circumstance who unintentionally become full-fledged super-villains. Likewise, I also liked the design concept they had for him, although I do agree he had a bit of a Human Torch look, although I can overlook this. After all, as Spidey observed, he also resembles an Oscar.

t: Finally, I appreciated that Mark's transformation into Molten Man via nanaomachines is a nice update from the original origin, and the fact the show also incorporated the later idea that Molten Man's body heat reaches near radioactive levels--or in this case high temperature.
Of course, another reason why this version of Molten Man using a combination of Mark Raxton and Bennet Brant into the Mark Allen character works is how his downfall has had an effect on his sister, Liz, and Mary Jane. While it could be argued that while Peter, if had been a more attentive boyfriend to Liz, might have helped Mark sooner, Liz and MJ must also feel some guilt over this. After all, Mark is Liz's brother, and she knew about his gambling problem better than anyone; it was only after he became the Molten Man and tried to kill Spider-Man that she finally confronted him on it. And MJ also knew about his gambling problem as his girlfriend; and yet, even though she realized that she cared about Mark more than she let on, you could say that her philosophy of "non-dating dating" was probably what prevented her from getting close enough to help him. But then again, as Harry told Peter, when it comes to addiction, sometimes those who have a problem ultimately have to decide to help themselves. Whatever the case, it certainly will have an effect on both character's development. In the case of Liz, it's likely that this will be just one more nail in the coffin of her and Peter's relationship, the others, of course, being Peter's double life as Spider-Man, his attraction for Gwen (and by the way, I'm probably not the only one who approves of the new "classic" look the show has finally given her), and Liz's own jealousy. For MJ, its a realization that she doesn't really want to be in non-committal relationship, as clued in by her seeing Peter and Liz embrace and her standing alone after Mark's arrest. My guess is that if a third season happens, and if something else prevents Peter and Gwen getting together, perhaps this will allow an opportunity for Peter and MJ to get closer as friends and find themselves becoming more than that much to their mutual surprise and misgivings.
The best aspect about this episode, however, was the Green Goblin. I've forgotten how Steven Blum's voice acting for the character is just so perfect at conveying the insanity, dark humor, and Machiavellian cleverness of the character. In the comics, it never really came off too well that such a flamboyant, in-your-face character like the Goblin could be a behind the scenes manipulator since both characterizations seem like such conflicting traits, but in this case it works very well, serving as a reminder that, prior to his being revealed as Norman Osborn and discovering Spider-Man's identity in the comics, the Green Goblin did attempt to control the criminal underworld. And of course, the mystery of his identity still deepens. We get a suggestion that Harry, in his conversation with Peter, had a relapse of taking "Globlun Green." However, since Norman Osborn was present during the transformation of Mark into Molten Man, this could also hint he's the Green Goblin as he is in the original comics. However, and this might really be out of left field, given that the Goblin knew how the Mark's powers worked and his newfound love of blackmail, I'm wondering if the show is throwing us another curve ball and that THIS Green Goblin is Miles Warren. After all, the Goblin did mention how Mark was "never in control" and echo of Miles Warren telling Mark that he was in control of his powers, not to mention there seemed like a close up of something that looked like the control button in Miles' hand. And since Miles is blackmailing Curt Connors and this Goblin blackmails Mark, well, there you go. As I said last time in my comments on "Gangland," the Jackal is very much like the Green Goblin in a lot of ways, and so having Miles Warren be the Goblin this time around could be a logical choice, and still maintain the idea that Norman is the real mastermind in that he manipulated both his son and his new top scientist into taking on the role to cover his own tracks.
As for the structure of this episode using each of the prinicple characters to have a series of flashbacks that led to the fight between Spidey and Molten Man, I didn't find it all that obtrusive or distracting, and it didn't break up the momentum of this episode one bit like flashbacks sometimes do. Flashbacks as a storytelling device, are tricky things to employ effectively, and in this case it was done right. We also got another instance of using quotes Shakespeare, in this case a scene Midsummer Night's Dream between Hermina and Helena, to reveal the supporting character's emotional state, in this case Liz and MJ. Unlike "Growing Pains" which made this seem heavy handed and gimmicky at times, here it works effectively, especially when used to compare and contrast the characters from the episode's beginning to the episode's end.