Before I start this review, I just want to say that Nanbaka is probably one of my favorite shows that I've ever watched, and I've enjoyed it immensely. I would love nothing more than to give it a 9/10 or 10/10, just because of my personal tastes. But that's not reasonable, so I'm going to be accurate in my review, and not go easy on this show. Nanbaka does have its flaws, which I was able to overlook, but you might not be able to do the same. Note: I'll try to keep this review as spoiler-free as possible, but there may be some spoilers. Also, this is pretty much a review for both the first and second season, which are treated more like two halves of the same season.
Story: 8/10
Starting from the first episode, Nanbaka seems to be sort of a comedy slice-of-life show about the lives of four flashy inmates in a flashy, maximum-security prison. The first episode does a very nice job introducing the personalities of the main characters in a natural way, as they interact with each other. There's no huge exposition dump in the first episode, as is common in a lot of bad anime. (There are some exposition dumps in future episodes, but they're still done naturally, and don't distract too much from the story.) Not everything about the characters is explained in the first episode, but they set a great base to work off of for future episodes. You can tell that the first episode is only providing you with the basics of the plot and characters, so that you understand what's going on, but you aren't spoiled for everything. It's a great storytelling strategy.
I was kind of expecting Nanbaka to just be a comedic, slice-of-life, episodic show, about the wacky misadventures of the prison inmates, as it advertises. It turns out that there are some over-arching story elements. In the first "season," there is a story arc that spans several episodes. When watching this portion, I found that I preferred the slice-of-life portions, with the goofy jokes and the simple character interactions. The comedy in this show is actually very funny and well-written. It's kind of an absurd, random style of comedy, with lots of slapstick and hilarious one-liners that come out of nowhere, leaving you laughing at how bizarre everything is. If you like that style of comedy, then you'll love this show. The comedy is the highlight, but the story eventually gets good, as well. The story is character-driven---it unfolds as you learn more about the characters. The first story arc gets a bit tedious, but it pays off at the end. Just give it a few episodes. The story arc in the second season doesn't have as great of a pay-off, but it's more interesting throughout.
Animation: 6/10
(Sigh) This is the part that I get mixed feelings about. I really wish the animation in Nanbaka was impressive and groundbreaking. But this is probably the show's biggest flaw. The animation isn't god-awful---it's not like there are glaring flaws or anything---but you can tell from watching that the budget for the animation was pretty low. If you're someone who is critical about animation like me, then you'll constantly be spotting places where they cut corners. Reusing animation, using simple patterns instead of drawing detailed backgrounds, cutting out parts of action scenes that would be difficult to animate, etc. It wasn't a dealbreaker for me, but these flaws were very noticeable.
There are good things about the visuals, though. The character designs are ridiculous and fun, matching the tone of the show. Warning: if you prefer your characters to look realistic, and hate crazy anime hair, then you'll despise Nanbaka. Personally, though, I love it. It shows a lot of artistic freedom---Why not have a character with an impossibly long, multicolored braid? Or a character with hair that turns into arrows when he gets pissed? Another fun thing about the character designs are how flamboyant they are. Everybody, including the male characters, is wearing nail polish, or makeup, or piercings. It's very refeshing in media to have male characters being feminine without any judgement. I also admire how diverse the cast is. There are characters with different shapes, sizes, skin colors, nationalities, etc. There's just a lot of creativity put into the character designs, instead of making them look like generic anime characters. I really appreciate that.
I also like the design of the prison they're in. Reminds me a quite a bit of Deadman Wonderland, and I'm sure that was an inspiration. Another fun thing is the unexplained sparkles that are in every shot, like someone just sprinkled glitter over the whole prison. It's not needed or anything, but it's a nice touch. Overall, the visual style is great, but the animation itself can be really lazy sometimes.
Sound: 7/10
Not too much to talk about here. The opening and ending themes are both very catchy and well done. Nothing else in the soundtrack is really memorable, but it's not bad or anything. One thing I don't understand, though, is why they decided to change the singer of the opening theme halfway through the show. Honestly, the first singer sounds a lot better---the second singer is kind of nasally and annoying.
Characters: 10/10
Now this is where Nanbaka really shines. The main thing that kept me watching this show was how attached I got to the crazy cast of characters. The four main inmates are the best. At the beginning, they may seem like stereotypes---the arrogant one, the otaku, the one who loves food---but as the episodes go on, they receive a lot of character development. All of the characters are written fantastically. The best part of the show for me was the genuine friendship and love you could feel between the four main characters. Even with their their quirks and petty squabbles, they care about each other, and support each other physically and emotionally. Even though they're criminals, these characters are so genuine and lovable that you wish they're real.
The side characters are great, too. Some get more screentime than others, but all of them are very interesting and enjoyable to watch. Like I said, the absolute best part about this show are the character interactions. That's the reason why I recommend it.
Overall: 8/10
If you can look past its flaws, Nanbaka is a great show. But it isn't for everyone. If this review makes you interested, then go watch it!