that is some form of the Serpent Squad that our heroes are about to take on. the middle figure is the Cobra, but I don't recognize the others. it's a rather funny battle, at least at first.
the cartoon really does capture the various personalities of the Avengers. Hawkeye and the Hulk are just really well realized. it would be neat to hear Hawkeye refer to Cap as "Methuselah" as he did in the comics, but overall he's perfect.
Cap's shield is a deadly weapon. the characterization of Cap is off to me, he seems far too dull and humorless here. a good soldier, but he wasn't a soldier or had the training they did. I'd like to see him lighten up a little.
Hank is a pacifist in the cartoon, and he quits the Avengers (I've read this story before). he hasn't realized Ultron 5 has done his own programming modification so he can complete his task of getting rid of evil and crime. which of course means eradicating humanity. he can't kill Jan though (and some of us know why that is as well).
the Hulk and the Panther bring the Red Ghost and the Super Apes in. I LOVE this Hulk. so nice that he's not monosyllabic and angry all the time. how on Earth did they sell that Hulk for so long? Ultron has "killed" Thor and is not quite defeated yet...