Is laying down in the grass staring at the sky a mediocre experience? Maybe some days. In others it will be exactly what you needed and didn’t know.
Give too much emphasis on curating and spontaneous gems will pass you by.
I’m writing this to my younger self as much as I’m writing it to you. I have no doubt my words won’t change your outlook in one go and that you have to learn this experience for yourself, but the sooner you do the fewer time you’ll feel to have wasted.
And remember it doesn’t matter anyway. If you’re an atheist, dying means you won’t feel or remember anything. If you’re religious, dying means an eternal existence. Either way, “wasted” time makes no difference.
It isn't even necessarily about watching "bad movies" on purpose. Even in the space of movies, one dice roll I've made is to watch the best movie of some genre I'm not particularly into. Even if it doesn't "convert" me to a fan of the genre this has often paid off for me. Another example is a lot of people get into musical ruts very early in life, often I think not even having a clue what the diversity that is out there is like. It doesn't take much to just make a random leap across the landscape to somewhere you've never been to check a new space out.
You definitely shouldn't waste your time on bad experiences deliberately, but with only positive and rewarding experiences you miss out on growing your own frame of reference and risk becoming blasé or completely risk-averse.
And good experiences can't always be planned or divined by browsing reviews.