The first season (or episodes 1-13 if you're watching on Disney+) is really quite poor. This is apparent fairly immediately too as you're hit by a dreadful disco opening theme. The animation isn't terrible but it's not good either, villains especially look bad, most notably Dr Doom and the muscle-bound Silver Surfer (serving a poor Galactus). Unlike the other Marvel cartoons there is no depth to any storylines, they're quick, easy, and very conveniently finished by having Mr Fantastic just saying something about science and you're done. It's a kids cartoon that can only be enjoyed by kids. It's super camp as well, in one episode Johnny Storm even has a musical number for no reason.
5/10
The second season has far better animation, dialogue and plots. It gets a lot more interesting as in the last few episodes there are a lot of crossovers with other characters from the Marvel universe. Perhaps with it being the same release years as other cartoons then plots could have interlinked instead of being repeated though (mostly with Silver Surfer). It's still far from perfect, especially with one of the last episodes just being a very lazy clipshow, but majorly improved.
7/10.
5/10
The second season has far better animation, dialogue and plots. It gets a lot more interesting as in the last few episodes there are a lot of crossovers with other characters from the Marvel universe. Perhaps with it being the same release years as other cartoons then plots could have interlinked instead of being repeated though (mostly with Silver Surfer). It's still far from perfect, especially with one of the last episodes just being a very lazy clipshow, but majorly improved.
7/10.