Isekais that you think are actually good and why

Here are my picks:

Ima Soko ni Iru Boku - the best isekai I've ever seen. Mature themes (war, children participating in military conflicts, many tragedies coming from it, dystopian dictatures) and good production quality. The show is well directed and with interesting story. Its characters are not that much complex, but complex enough to blend well into everything and participate in the storytelling process.

Digimon Adventure - one of pioneers of the genre. Exciting world, good character designs, unique atmosphere and setting. Fun to watch for literally everyone, not only fans of the genre or teenagers.

Kono Subarashii Sekai ni Shukufuku wo! & Kaminaki Sekai no Kamisama Katsudou - for their humor, full of gags and hilarious situations, and take on classic DnD adventure. Everything mixed with very nice visuals and interesting direction (mostly when it comes to KamiKatsu. Speaking about KamiKatsu, the concept was and still is fresh, unlike 90% of copypaste generic isekais, lol.

Tensei shitara Slime Datta Ken - for it serving a wholesome atmosphere, and mix of a classic, generic isekai, but enriched with various many features, to the point of making it feel unique and fun to watch even by people who are not particularly fans of this genre (like me).