Josef wrote:You could also say:
We would have appreciated it highly if this review had been signed.
Thank you for the additional way of saying the sentence.
I like to see "highly" after "it" and not "appreciated it if" kept so closely one to another.
"Appreciated it if this" is hard to say for me.
In addition you've led me to say the sentence this way
We'd have appreciated it highly had this review been signed.