If this is about judging a game on a mass scale to objectively determine the worth of a game, then the process is objectively simple:
-IGNORE SUBJECTIVE DATA AND FOCUS EXCLUSIVELY ON OBJECTIVE DATA
Use Sales Figures over Metacritic. Anyone can be a critic, but only the most outspoken of the lot care enough to actually say anything.
If they're "professional", then know that their credibility is always suspect because they can (and have been) bought out. The only opinion you should ever trust implicitly, is YOURS.
There is a catch to this: Unless they're seeing wild success (compared to THEIR PREVIOUS ATTEMPTS, note the frame of reference), most game companies are NOT going to share market and sales information with anyone outside of their company (as a matter of security, and to enhance marketing. Remember: Marketing is most effective when people act on emotion, not logic). So even here, attempts at objectifying a game's true value is going to be hindered considerably.
Besides, popularity is already strongly correlated with financial success anyway (economists can refer to effects of a "Network Good". The most profitable games of the past decade have their multiplayer and online populations to thank: Halo, CoD4.x, WoW, and anything Zynga copied all show this trend. Accessibility, social entrapment, and grind combine to create profit-engines).
Quality and "artistic merit" (just take it as it's intended without the sense of pretentiousness) have historically fallen SECOND to that. Fad-mentality can make or break entire platforms, as the Nintendo Wii can attest; let alone games.
However,
If this is about using popularity as the main metric to determine whether one purchases a game or not: just don't. Personal taste MUST COME BEFORE ANYTHING ELSE in a hobby. Common sense, I know, but it bears stating here.
If we all used popularity as the primary means of judging a game, then the gaming market would just stagnate and die the instant we start getting bored with it.