A critical issue.

Overall, it's mediocre, and it's also filled with rather uninspired filler episodes. The second season has fewer filler episodes, but it's still not great.

Since we're talking about filler episodes, let's abstract from this discussion and the specific title – I've seen countless opinions online that filler episodes in series or cartoons are bad and don't deserve to exist.
Of course, I don't agree with that. If you prefer to see instead of filler episodes how another very original hero defeats all enemies for the hundredth time/marries his classmate/dies, then you are probably still young, and this is new to you.
Am I right, guys? Skipping non-plot content – I wouldn't have believed that such a thing exists! But there are people who only watched the last season of Breaking Bad because of the hype; may they rest in peace.