Fish not being bash compliant was a deal breaker for me.
I use zsh with https://github.com/zsh-users/zsh-syntax-highlighting zsh fish like syntax hilighting and am much more happy.
Fish is optimized for interactive (the i in "fish") use. Not exactly the same as bash-compliance, but if you have bash-based tools (like virtualenv but without counterpart in fish land), check out https://github.com/edc/bass. Bass allows you to use a bash tool in fish, by running the tool in bash and transporting changes in environment variables back to fish shell.