Fish breaks compatibility with traditional shell languages. The syntax is a bit different, the variable expansion rules are a bit different, etc. It also gets rid of a bunch of features and configuration options, such history expansion ("$!!").

The positive side of this is that fish is very simple and has a very pleasant experience out of the box. And this is not just about having "good defaults" - its also about having a good design that encourages having one way to do things. That said, an interactive shell is a very personal thing. The only way to really get a good feeling is to install and check it out.

I used Fish for about of year. But I ended up recently switching back to zsh. Stock Fish is far more useful than stock zsh. However, the community around zsh is far more active and I found that most of the functionality that Fish contains and zsh lacks that there are plugins to achieve the same effects.

I'd encourage you to check it out. The scripting language in Fish is the best I've ever used for a shell. But it's also incompatible with Bash/zsh.

> what value Fish adds above prezto/zsh. Could anyone help me out here?

- not assuming you're using an outdated terminal so doesn't waste a column when using a right-hand prompt?

- lots of async calls, thus really fast.