Fish is a bit like the Mac of shells. Stuff just works and its easy to use while flexible. Lots of little details are well polished.

The downsides are similar to Mac. Less standard/compatible with other stuff. Zsh seems more like a traditional shell. Meaning it is far more complex. Fish really aims to keep simplicity.

I have used Fish for many years and swear by it but I am also not the kind of guy who writes long shell scripts. I use regular programming languages for that. For me fish is mainly about having a shell that works well in interactive use.