Konosuba is pure, unbridled stupidity. Kazuma and crew are so unbelievably lacking in their mental faculties that it is a wonder how they are even capable of putting their own clothes on every day. That they even know how to breathe is surprising in its own right.
Where most other anime in the fantasy genre-- Danmachi, Re:Zero and others of its ilk-- attempt to be absolutely and relentlessly serious at all times, Konosuba does away with the very notion of seriousness. It exists solely to be laughed at. And sometimes it does a pretty OK job at creating said laughs. It never aims to be a 'good' anime (least not in the traditional sense), and criticising it for not being such is kind of missing the point.
It just becomes a bit difficult to keep laughing when they repeat the same jokes for the fifth or fiftieth time.
Darkness is a thundering masochist who mentally orgasms and gets foamy-mouthed whenever she is treated poorly. The first season already made this joke several dozen times, so I get it. Kazuma will threaten her by promising to do unspeakable (!) things to her body, and, the deviant that she is, squirms in delight! No, look, I get it already-- I really, truly do. Her mind is so perverted that she will twist a friendly conversation into a suggestion of her being sexually assaulted by monsters and--- PLEASE, KONOSUBA. I GET IT. I get it, OK?
For as much of a joke as Konosuba's characters are, there is only so much comedy they can create by repeating the same punch-line until the ends of time. There are other, more interesting things that can be done with Darkness' character, surely. If this were pornography then maybe, perhaps, her characterisation would get a pass, but comedy requires considerably more effort than "oh gee golly I am like so horny right now."
Aqua, as tantalising as her mini-skirt is (and I have spent many a moment admiring her womanly curves), falls into much of the same issues, with her two defining traits being that she is a narcissist with an ego the size of Darkness' breasts, and a crybaby who falls on her knees and wails at the top of her lungs when she doesn't get her way. Her gags, almost invariably, follow a pattern of these two traits: she uses her status as a goddess to demand favours and respect, and then breaks her character and cries immediately after. A little bit more involved than Darkness' 'gag', sure, but it is still repeated to the point of nausea.
Kazuma is likely the more interesting of the lot, since he at least exists as more than a vehicle for a single joke. He is not developed by any means-- lord, no, he is a complete dunce from beginning to end-- but his frequent switching from idiot to straight-man does at least provide some variety to the gags. Kazuma is a jerky little twat, incapable of respect and prone to molesting the opposite sex, and his assertive nature does well to set him apart from all the other spineless protagonists of the genre. His over-reactions to all the ridiculous nonsense around him (often the direct result of Aqua's or Darkness' actions) are often still amusing, too, even if 'dude yells at stuff' may not exactly be the most artful style of humour. You almost feel bad for the little bugger - I would probably want to off myself in his situation, too.
There's not a whole lot to say about Megumin, considering she is pretty well non-existent for 90% of what happens in the second season. She's unquestionably the most sane of the four (though that isn't saying a whole lot...), and the one least susceptible to repeated gags. While the first season pushed it a bit by making her defective explosion magic and chuunibyou nature a recurring theme, the second season has next to none of it. And that's a good thing. I just wonder if, cute as she is, she might be a bit too normal the second time around.
Konosuba just never capitalises on what made absurd comedy series like Osomatsu-san and Gintama so clever. There is wonderful opportunity here for it, as one of the only non-serious fantasy anime, to take the piss out of other titles in the genre and properly satirise them. Part of the joke is that the Gang of Stupid are woefully incapable of combat, unable to progress as one typically would in an MMO or fantasy world, and are able only to defeat monsters and enemies through luck and by surprising them with their colossal stupidity, provided they don't just scream and run away altogether. That's an amusing reversal of the genre's tropes. But that's all there is. There's no actual "satire", no parody to be found in Konosuba - it is standard manzai comedy, living, and dying, by its own strengths and weaknesses.
That isn't to say that Konosuba is without merit, or that watching it can't still be a fun time. If you enjoyed the first season or just want a short, easygoing anime that doesn't require much thought or focus, then, hey, it does its job just fine, even if it may at times feel more like a greatest hits compilation. Konosuba is a big, dumb show and it knows it. I just don't think that being dumb is an excuse for laziness.