To my surprise, I didn't like it. Season 1 was great. Season 2 has changed a bunch of stuff and I don't think it works.
Fist of the North Star is a maximum-testosterone show of exploding heads in a Mad Max post-apocalyptic future of a Jesus-like hero who's killed thousands of people with his bare hands. Those are just his victims on-screen, by the way.
DD Fist of the North Star (Season 1) is a parody of this, with Kenshiro and his brothers showing that being a musclebound superhero with a death touch isn't very useful in day-to-day life. They work in a convenience store. They're inhumanly strong and inhumanly stupid. This is a solid comedic foundation and the show made me laugh a lot. Even the theme song is in on the joke.
DD Fist of the North Star (Season 2) uses the same goofy art style and ostensibly similar gags, but they've moved the show's foundations. Kenshiro and his brothers aren't stupid! Well, sometimes they are, but their stupidity is only occasionally the basis of a gag. Similarly their goal isn't getting a job, but instead to get admitted into school and spend time with the school nurse, Yuria. This is less funny. Yuria's okay, but that's a thinner basis for an entire series. Our heroes' characterisation has thus been shifted from "stupid" to "lazy scumbags", with Toki in particular having been transformed into a sleazy underworld crook. That had potential, but unfortunately I don't think our heroes have become noticeably evil either.
Ryuuken's been given a bigger role. There's nothing wrong with that, but unfortunately one of his main jokes this time is that he's gullible and will pay billions of yen for anything at the drop of a hat. "Gullible" is good, but the amounts of money being thrown around are so silly that none of it has any reality and so Ryuuken's debts are meaningless. They're just comedy noise in a silly show where nothing matters. Conclusion: I don't care about them.
The difference in theme songs makes it all clear. Season 1 has a brilliant opening sequence that tells you what the comedy's going to be about. Season 2 has a boy band doing some random song that I usually skipped. (I enjoyed the closing title sequence, though.)
Then there's Strawberry Flavour, which is a four-minute bit at the end of each episode with a different production team and non-deformed art. It's riffing more directly off the parent show, portraying real scenes from the original and drawing the characters as they really were. It's silly. I didn't bust a gut, but it's okay.
In fairness, the show isn't completely laugh-free. There's stuff I liked. Roah's girlfriends are funny, with the titan in ep.3 and then later his pig-faced wife. (I particularly like the former's girly voice.) It also took me a while to realise that I didn't like Season 2 as much as Season 1, so I happily watched the first few episodes without noticing much difference in the jokes.
It's not a terrible show. It's still directed by Akitarou Daichi. It's still got a furious gag rate and lots of pace and invention. It's also got lots of parody, e.g. Yokai Watch, Detective Conan. I admire the principle of shaking things up and not just resting on your laurels, but unfortunately here that's produced a parody show that I don't find very funny.