I absolutely love using https://movielens.org/. The more I've rated, the better its predicted ratings have gotten for me. It doesn't seem to be popular enough to be as gamed as some of the others. Be honest with your ratings, and it will steer you in the right direction. Don't give Rashomon 5 stars if you didn't like it. If Wedding Crashes is your favorite movie, that's 5 stars for you.

When I'm trying to find a movie that my mother-in-law is going to like, I start with That Thing You Do or a Knight's Tale and I check Similar Movies.

In my opinion, https://themoviedb.org/ is slightly better than the alternatives.

I've used metacritic for years, it's much better in my opinion

I take a look at letterboxd but it is too unreliable to big titles.