I feel in season 5 and 6, the humor gets much worse. It doesn't come off as clever when you're making fun of SJW's, or fanart and shippings, or how the world is garbage today and just overall political references when you do them every other episode. I would be okay with this but I also feel the other humor they have isn't written as well as it used to be, plus I'm not big on how the Wattersons are written now, plus Gumball and Darwin's new voices suck.
I guess my main problem is that they up the ante on pop culture references and even toilet humor at some points but forget to write funny dialogue and when they talk about something serious (like The Parents or The Transformation for example), it is executed very poorly. It's weird too considering some of the season 5 and 6 writers worked on previous seasons or the whole show in general. Maybe it's with a lot of the writers who come in around late season 4-6??
Also noticed the art direction in season six looks cheaper to the point where it's very noticeable. I don't know what's going on but the peak of the show was around Season 2 through 4.