To be honest, I love BTTF and BTTF3..but BTTF 2 is not something that I would argue well of.
Being blunt, I don't believe BTTF is as big of an IP as how Mario or even Potter is. Regardless of Age, Potter and Mario touch multiple generations of individuals and groups. BTFF, has it's fans; but it's not to the level of what I would argue, are evergreen IPs.
Star Wars, Hello Kitty (merch alone), Potter, and Mario, are; because of how they have reached so many audiences.
Back to The Future, is an IP I love, but I am not going to be singing it's praises. Hell, I put that mindset similar to Jaws, as outside of the first and maybe the second..there isn't much there that is justifiable for me to say it's a cultural phenomenon.
They deserve marks in what they did for the industry, yes. But I am not going to sit here, and say that they are perfect for modern-day audiences.
I would argue other things though.