No season is bad in my opinion and I respectfully disagree with people saying that certain seasons are "bad". They're trying out different angles of the horror, thriller, ghost, supernatural etc genres. Of course there's going to be seasons some people like a lot less than others because not everyone is going to like all of those genres and not everyone is going to agree with the style it's executed in or the casting choice.
I have least favourite seasons and most favourite seasons but all are loved. The best thing about each season is seeing the sheer talent and versatility of each actor as they return to play a new character. It's such a unique experience. The fact that I could watch Apocalypse and not feel like I was watching an actor play multiple characters, but see multiple vastly different people with coincidentally the same face is crazy awesome.
I look forward to each season as it gets released and I'll be very sad the day they stop.
If you haven't watched AHS yet and are into supernatural types of things you HAVE to watch this.