I had it twice a while back I think. It was surprisingly better than I expected, and I didn't notice much of a difference. That said, I rather have real meat. But it's definitely a good innovation, especially in the distant future when meat or food in general will probably become more scarce.
Curious to try the Impossible Whopper as well, since there's a Burger King a few blocks down from me. But I never like the whopper in the first place. So I likely will not like it regardless.
Enjoy any good things, even the little and menial ones, as you will never know what impending distresses could descend upon you in a moment.