The average rating (out of 10) is also flawed. It only averages reviews from reviewers who give a number grade. Outlets like say NYT, do not score a movie, just write a review, so they do not contribute to the average rating (out of 10). But atleast by reading you can gauge whether a review is positive or negative so the Tomatometer is counting just that, the percentage of reviews that are positive.
Metacritic is also problematic. They actually read the review and assign it a number grade ON THEIR OWN.
The best possible gauge of critical reaction can only come at the end of the year. The end of year critics polls and Top 10 lists are the best source of critical acclaim, as that is where the passion shines through. So true critical reaction, frankly is gauged only at the end of the year.
Exhibit A - Harry Potter 8 - 96% on RT, Average Rating 8.4, MC rating 87/100. You would think one of the best films of the year? Did not make the Top 50 in any of major critics poll of the year. Not even the Top 50 yeah.
Exhibit B - Mullholland Drive - 81% on RT, Average Rating 7.4, MC ratin 81/100. Nice positive reaction right? UNIVERSALLY hailed as a gigantic masterpiece, topped every single critics poll in 2001 as the best film of the year, top every critics poll in 2009 as the best film of the decade. Now regarded as one of the greatest films ever made.
So the end of the year showed us what critics really thought of Mulholland Drive and Harry Potter 8, their reviews did not.
So end of year lists are your best indicator. And even later, lists like Sight and Sound ( a poll run once every decade) gives you a broader view of how films have aged.