Best isekai worlds?

[Ulfgeir]

Stephen Donaldsson had 2 different isekai worlds in his book-series. I wouldn't call either one of them good though.

 

[Paul Farquhar]

Star Trek TOS - from the perspective of USAF Captain John Christopher.

 

[Dannyalcatraz]

Multiverse (Marvel, DC, Moorcock, others)
Fractal universe (Marvel, DC)
Flatland
The Matrix
Guardians of the Flame (Joel Rosenberg)
D&D cartoon
Connecticut (Mark Twain)
The Dragon and the George (Gordon R. Dickson)
The Future (Samurai Jack)

 

[Necropolitan]

The Wandering Inn (it's a free webnovel and my favorite ongoing fantasy book series)