Fish shell is great, but the more I've used it, the more incompatibilities I've found:

• Can't use subshells
• Can't use bash syntax (it would help if bass would process all commands by default)
• Can't use bash completions (there's a script to do that, but it makes start very slow)

Other than that, it just works by default (unlike zsh) and it works even better with an easy-to-install Tide