Disclaimer: I was a child in the 1070's, when the ORIGINAL Fantastic Four cartoon was produced. As such, I have been spoiled and have a point of reference not available to all.
Susan Storm Richards, as characterized here is a train wreck and a travesty to the Invisible Woman of the comic series and of the original cartoon. Sure, they have focus groups and PC consultants who are telling them that making a stronger, dare I say, b*tchier Susan will attract more of a female audience, but that's completely wrong for the group dynamic and absolutely awful writing from the ground up. The Fantastic Four started as a comic book in the 60's, when women typically worked as either professional subordinates, as housewives, or both. In terms of power, prestige, and position, they were all but invisible. What made the original Susan Storm so brilliant is that while she possessed a mild personality that rendered her maiden name a complete irony, she was given the strongest power of all - invisibility, which later expanded to include invisible force. Her character was a metaphor as to how the unseen woman was often the most powerful person in the room, seeing everything and being able to manipulate the situation with tools that no-one saw. Sue was a woman who didn't need to get hysterical because she of all people knew that things weren't always what they seemed and that when you can't be seen, patience is your ultimate ally. The Susan Richards portrayed here is actually a weaker person than the original (fainting? REALLY?), having none of her calm or poise and where once was self-assurance, we find a diva's bravado, screeching "Look at me!!" to the world. Yechhh.
Reed Richards is a bit more nutty professor than the square-jawed team leader I remember, but the fit is surprisingly believable, thanks in large part to the fact that he never gets too lost in the science to forget about the larger issues at stake. Johnny Storm is the same irrepressible young buck he's been since Stan Lee first conceptualized him, meaning well but too full of mischief to ever let things be quiet. Last and best is Ben Grimm, test pilot turned golem, the gruff yet lovable blue-eyed Thing. Yes, he has a hard time fitting in this civilization built for human usage, but he covers it all up with a quick grumble, a forgiving heart, and the good sense to value who he is more than what he looks like.
One thing that I don't enjoy is a lazy trend I see in the animator's pencil. What's with turning everybody's chins into points in some places? Are they supposed to be half-elf or something? That kind of slacker work would never make it at Pixar, that's for sure.
Overall, I think the show is worth continued watching. At the least, it's nice to see a cartoon that isn't totally geared to 10-12-year-old crowd.