The criticism is that in creating the midichlorians the force became less metaphorical and more literal. Before TPM the reason the Emperor lost wasn’t because he had fewer “force points” than Luke or Vader it was because of a grander poetic narrative that some felt was cheapened by having the bigger number go brrrr

I mean, they were fairly unpopular among the fandom when the movie came out, and I think they are still somewhat unpopular.