Anime

Zenshu is killing it this season. Anime-original story, tries to actually connect with Natsuko Hirose's "real life" (not just focused on the fantasy world but also her experiences before getting Isekai'd), etc. etc.

Reincarnated as a Slime is my favorite somewhat trashy isekai (as in: it follows all the tropes but otherwise the animation quality is actually really good). Its an "overpowered" show where the main character rarely comes across a real challenge though.

I'm a Spider, so What?! is a fun boss rush that had a deeper than expected story. Main character always wins of course, lol, but I think it "felt" like a challenge as she learned combat of this new world?

Overlord is a "take over the world" / "Kingdom builder" (Slime also is a kingdom builder but its not as good as Overlord). Overpowered once again, literally no one in the new world can challenge the main character. But I don't think that's a bad thing for Overlord, it allows the plot to focus on kingdom building / alliances / kingdoms rather than the fights.

A grossly underrated Isekai is: "The Weakest Tamer Began a Journey to Pick Up Trash". Its basically just this young girl talking to herself for ~12 episodes as she's forced to run away from home. https://www.youtube.com/watch?v=-biFNoRk-3I . Still, the people she meets on the journey are all helpful and optimistic. This isn't a battle anime (she runs away from pretty much every fight), and she very much relies upon the kindness of strangers. Its actually quite unique for an anime since she doesn't have nearly as much "Because I'm the Main Character" energy, even if she gets a few special friends along the way. Very much an "underpowered" main character, who has to mostly dig through trash, cry, find friends and run away constantly.

Re:Zero and Jobless Reincarnation are probably the most popular Isekai. But I didn't like them. I figure I should mention them though.