It's a cartoon, but it's not for kids. It makes you laugh, but it's not a comedy. Categorizing Bojack Horseman is like trying to catch your shadow, except for one category that it does fall into. Brilliant!
There's too much to go into in one review & much has been said already. Yes the first series was more towards the comedy side, the 2nd series was darker, series 4 was very imaginative. However, what I do not agree with is the claims made about Bojack's bad behavior. Whilst he is undoubtedly everything people say that he is, often he is the victim that ends up saying sorry. A case in point is Tod's girlfriend, Emily, where Bojack ends up apologizing to Tod for having sex with her, yet Tod rejected Emily & Emily made her situation very clear to Bojack. This was AFTER Bojack went out of his way to make it easy for Tod to get together with Emily!
Another example is Bojack's "daughter" Hollyhock. Her string of fathers blame Bojack for her overdose & he apologizes, despite the fact that the overdose was nothing to do with him & was the product of his mother's addled thinking.
The fact is the series often tolerates a-hole behavior from others & glosses over it, but Bojack never gets a pass, either in the story or from the judgement of the audience. You could argue that this reflects real life, but for Bojack to not only be so passive about some of these situations, but seems to be the one to initiate the self inflicted humiliation necessary to apologize for things either partially, or even fully not under his control, seems sadistic. Even the Sarah Lynn arc ended up with her getting clean ONLY so she could reduce the tolerance she'd built up to drink & drugs which would make their effects more intense when she started using them again, which she clearly intended to do. Bojack may have played his part, but Sarah Lynn was merely using him as an excuse.
Since I've not finished the series yet I'm not sure if there's a point to all this, but so far I find this an annoynace that he is presented in this way.