I check through RT, IMDB, Google Reviews, Letterboxd and average them all out.
You have to dig into RTs reviews and look at the critics average and the audience average (you can often find a film with 80% critic approval and 20% audience approval .... and the site will only post the critics rating)
When doing your research ... also look at the number of votes ... if 100 members voted 90% chances are those are all movie production promoters boosting numbers. IMDB usually has higher numbers of votes for everything which gives a more reasonable average.
I get what you're saying, but IMO a 2 hour movie is too low stakes to warrant spending more than a minute or two glancing at reviews, which is why RT and IMDB are nice, even if the summary score isn't totally reliable.
Am I interested in it from a quick synopsis or trailer?
Are the reviews generally at least mixed or better?
If the answer to both those is Yes, there's a good enough chance I'll enjoy it to give it a shot.