As far as light, digestible shonen stuff goes, this is pretty good. The soundtrack, voice acting, art direction and even the animation are pretty good. Where I think it falls flat, I think, is the characters. On the one hand, early on, it's pretty good at surprising you with their disposability. Some cliche types I thought would be in it for the long haul get snubbed out which keeps things a little interesting. But ultimately what stops this show from being great, mostly, is the main character. Gabimaru is a really bland and uninteresting character. Generic Sasuke 2cool4u type. The only quirk is liking his wife but it's almost mechnical in how they use it to justify him doing heroic or likable things - there isn't a sense his relationship is indicative of another layer to his character underneath all the trite power level stuff. It's just that he's the protagonist, so his motivation is his wife makes him Feel Like A Good Person so he Acts Like A Good Person. It's pretty terrible, actually.

Compounding this are 1) the fact that most of the other characters are more likable and would function better than him as protagonists and 2) the big twist of the story is just sort of thrown at you in the last episode with no pageantry. Would have actually been a cool, emotional moment and surprise but no I guess they thought it would as a hook for a second series?

I say most of the main characters, but the female lead is similarly very dull. I didn't dislike her as much, because I prefer more normal, banal characters, but I'd be surprised if the average person found anything to like in her really. She's a good guy. Her character progression begins at episode 1 and ends at about episode 4 or 5. So she's a little boring, but the ninja girl...Hoo boy, she was badly done. I think I just hate the archetype of smarmy, obnoxious girl only out for herself, but it was especially bad in this case. She's entirely without depth - which is fine, but they give her the "mature, pragmatic, voice of wisdom" moment at the end and it is completely unearned. I would say a pretty dreadful character.

That said it's worth a watch for the other reasons I mentioned - like the aesthetic of the island and the monsters. They feel like they were influenced a bit by Sekiro, with the perverse dharmic mysticism that's present, a degenerate immortality and so on. The problem is, I think, that the premise of the story, that the criminals can earn a pardon for succeeding in their quest, feels entirely ridiculous after you see that the island is a horrible death trap. The main character girl is babbling on about getting a pardon for Gabimaru in the 13th episode - so many of people have died, you're all gonna die, why are you bringing that up?! Who cares?!

The pacing is very good though, so you don't feel like you've wasted your time. And I love the opening! Thank you.