When I first saw this series, the animation didn't impress me, unfortunately. I must have been spoiled by the quality of Fox' old X-men cartoon (at least the first few seasons of it, anyway), but as it progressed, I found myself overlooking most of the problems and actually enjoying it. Just like the comic book, the series doesn't waste any time in grabbing your attention. It also holds onto it and doesn't get boring. The action comes fast and furious, and the character interplay is quite enjoyable, and to me that interplay is a large part of what makes or breaks a show, especially one like this. Unfortunately, though, one of the few problems I'm having difficulty getting past is Tony (Iron Man) Stark's constant whining. I don't recall him ever being like this, constantly pointing out that the mansion is HIS every chance he gets, rubbing it in everyone else's face that it's HIS money that pays for its upkeep and all. When you're in a business like the Avengers are, he seemed to know and accept (at least in the comic) that property damage was going to come with the territory. If I were his team mates, I'd get pretty tired of him constantly harping about it. He offered the place as a headquarters. Stop complaining about it every time it gets a little beaten up. He also seems to think that because he offered the headquarters he should be able to boss everyone else around on missions. Just because he pays for the equipment doesn't mean he is the most qualified to lead the team.
As far as the other characters are concerned, I think the creative team has done a fantastic job with them, holding them true to their comic book counterparts. I especially like Thor in this series. His asides and quiet comments, (like the one about the mansion having its own voice and being quite unsettling) help make the show fun, and let's face it -- Asgard looks a lot better here than it did in the movie. Hawkeye has definitely kept his cocky bravado and the way the show weaves in his relationship with the Black Widow is proving to be quite well done. Janet is impressing me as well. She may be small (most of the time) but she certainly is no light-weight. Thor said it best, I think, when he told Tony "Remind me never to incur her wrath". If she inspires such respect in the thunder god, she must be formidable indeed. The Hulk is ok, I guess. I'm still not used to him being able to talk so well but I guess a lot has happened since I last got into comics.
Speaking of a lot happening, I'm still not sure I care for the Black Panther using all these vibranium weapons, either. He always struck me as the type to never need them. Be that as it may, though, I have always liked the character and I'm glad to see they brought him in. Giant Man, on the other hand, I could do without. He seems redundant on a team that already has "the strongest one there is" in the Hulk. I've always preferred Hank as Yellowjacket, he seemed to go along better with Wasp as that character.
Of course, where would the Avengers be without Captain America. He has more experience as a fighter and is the more logical choice I'd think to lead the team. Will we see problems develop between he and Tony as that becomes more obvious? We'll see.
And of course, every hero team has to have its cast of super villains to go up against, and this one doesn't fail. Baron Zemo, Arnim Zola, the Enchantress, Kang... the list goes on and on, and they all seem to have their own agendas, whether they're working together or not, so it promises to be interesting for quite a while to come.
The artwork on the series is good, the storylines are interesting, and the acting is, for the most part, better than I'd expected. I still love Thor's calling out "For Midgard!". When he does, it always gives me goosebumps, because it's so effective. When he gets that angry, you KNOW someone's butt's about to be sent into the middle of next week...
On the whole, the show is doing a great job so far, even if it's only one season old. It's got a lot of promise for a long and interesting future.