It's an isekai story, but it's a bit odd. There are several ways in which you could call it two stories in one. This is interesting and I enjoyed the show, but those splits aren't all good.

As the title announces, our heroine is a spider (nameless except in the end theme song, which calls her Kumoko). She wakes up as one of thousands of cannibalistic siblings in a dungeon that's crawling with monsters. She's one of the smallest, puniest monsters you could find... but she's got human intelligence, inherited from a now-dead Japanese schoolgirl. She also has a loud, fun, hyper-enthusiastic voice actress (Aoi Yuuki).

Having no choice in the matter, Kumoko goes dungeon-crawling. The bad news is that everything in the dungeon is extremely CGI (albeit cel-shaded), but the good news is that this sub-anime has the best fights. Holy shit. You can go berserk with the action scenes when it's all CGI, while almost every single Kumoko fight is terrifying. She levels up like nobody's business, but it doesn't help. Halfway through the series, she can teleport foes into magma. A few episodes later, she attains immortality. That might sound cool, but unfortunately this is a fantasy world where your enemies also have access to all these skills and power-ups. If you've annoyed the Demon Queen, mere immortality won't save your arse.

This is a laugh. Simplistic, but entertaining. There are plenty of isekai out there that don't even aim this high... and that's only a fraction of this show.

At the same time, though, we're also following the adventures of Kumoko's other classmates. They've all been reincarnated too. Most of them are human. Most of them kept their original genders. It seems likely at first that none of them are evil. This half of the show has much more politics, worldbuilding and mysteries. No one's as entertaining as Kumoko, but there's a big, slow-burning plot and plenty of puzzle pieces for us to think about.

Naturally, we're waiting for the show's two halves to meet. When will Kumoko meet Shun, Kanata, Fei, etc?

We wait. And wait. And then, eventually, we start noticing that the show's been playing games with us and we're going to have to re-examine a whole lot of assumptions. Our notions of "goodies" and "baddies" are at the heart of those, incidentally. Kumoko's cute, funny and the show's title character, but she'll kill and eat anyone (because not doing so would be a waste of food) and will have a debate with herself while wondering whether or not to stop bandits from butchering some travellers. She describes war as an all-you-can-eat buffet of delicious, EXP-rich humans. (I'm quoting her.) Does this show contain any good people fighting unambiguously on the side of good? Does such a thing even exist? (Horrifying evil bastards are definitely present, though.) Powerful people are extremely worrying, whether or not they're currently your allies.

I found this fascinating. It's taking the simple, linear first half and twisting it into something far nastier and more unpredictable. Unfortunately, though, my reaction to the last episode was "stupid communications failure". A lot of trouble could have been saved had people talked to each other. I suppose my best defence of the show (so far) would be that when it comes to people like the Demon Queen, it's unclear that saving human lives is even on her radar. That said, though, there's clearly a ton of plot still to unfold from the original novels and I'm sure the anime's fans are demanding a Season 2.

Then, alas, we have the animation quality. The first half was Very CGI, but this gave us amazing fights and high-quality action. Also, in fairness, that's only the monsters, with the humans (and elves, etc.) being properly hand drawn. Unfortunately, COVID-19 hurt the production schedule. It had been meant to air in 2020. The last few episodes fall off a CGI cliff into dead-eyed plastic-looking dolls... and even then ep.24 missed its broadcast date. I'll quote Naoya Fukushi, one of the show's CG assistants:

"There are a lot of insensitive tweets from people who don't know the production situation. The outsourced animation on multiple episodes completely broke down, and Millepensee had to redo it all from scratch. The staff ended up being too busy for the later episodes that were set aside for them, which is a large reason for the poor quality. The staff are quite literally killing themselves to deal with this. Please be patient with the delay..."

"I do agree with the sentiment that regardless of the situation at the studio, what ultimately matters is what gets broadcasted. No matter what the reason, missing the broadcast is heavily frowned upon. But I made this tweet because I just wanted people to know that my friends' studio is battling desperately for the sake of this anime. And the people who are slinging insults won't stop until someone takes their own life."

This really hurts the show's most important episodes... but enough said. I'll move on.

Is this a good anime? Good question. The best way to describe it might be "lop-sided". When it's good, it's excellent. There's a lot of meat to get your teeth into. At the same time, though, it's full of halves that don't fit together. Do you love Kumoko? Well, you might find Shun, Kanata and Fei a bit boring. Do you love heroes and straightforward adventures? Get ready to have your feet kicked out from under you. Do you love cool action scenes? I have good news and bad news. Do you hate CGI anime? Steer clear at all costs.

I'd watch a second season, but I'm nervous about where the show's morality will go next. Will it all descend into a big swamp and I won't care any more? The show's definitely worth talking about, though.