Ugh. Then I understand why you might feel that way, there is a lot of progress in the show. First of all, they more or less drop the episodic format, after the first season the next seasons have much more of a linear progression. And yes, there is 6 seasons. They realised after the first season that some people were taking it as an excuse for Bojack being a jerk, and they incorporated that as a rather central theme. Especially in the later seasons. At some point one of the seasons (I don't remember which one) is kind of like a deconstruction of previous seasons in a sense.

By the way, I didn't like the first half of the first season and I stopped watching it until someone convinced me to start watching it again, and it just gets so much better.