Scripts will still work as long as they have the standard #!/bin/bash at the top.

Aliases - in .bashrc - unfortunately will need to be replaced by Fish functions; defined in the "~/.config/fish/config.fish" file by default.

The only real thing that keeps tripping me up with Fish is that it doesn't support shortcuts like "!$ ". I keep on typing that in, but due to the nature of Fish, it can't (or won't) recognise it. But the excellent history functionality does make up for this a fair bit.

Having said that, Fish is by far the best shell I've tried. I gave zsh a go for about half a year and got fed up with the autocompletion and general slowness. As a shell, Fish just behaves quickly and fairly naturally, with few exceptions (!$ ...).

I highly recommend it as an improvement over bash.