In theory, Metacritic is a great idea. A single site where I can find every published review for the media of my choice? Sure, sign me up.
The dark side of Metacritic, though, can be found in the all-powerful Metascore. These two digits comprise the average of every posted review, and, as we've seen in countless arguments throughout the decades, there's no "industry standard" for this type of mathematical evaluation—nor can there ever be. The equivalent of a 100-point score for USgamer (5 out of 5) is much different than, say, a 100-point score on PC Gamer, since their scale goes all the way to 100.
These Metascores would be a slight annoyance if they were only used for the sake of Console Warrior pissing contests, but, for a while now, they've had a much more insidious impact on the lives of developers. They often control the fates of bonuses and future projects, which puts unnecessary pressure on both devs and the people who review their games. And the Metascore can be an especially tricky proposition if you write reviews for a site with an atypical scoring system. When I worked at 1UP.com, which used a letter-grade scale, I remember our evaluations being transformed into numbers much lower than the ones we would use if a 100-point scale was forced upon us. A respectable B amounted to a 75 on Metacritic, which always seemed more than a little off.
When it comes the review aggregating business, there's definitely room for competition, and the new website OpenCritic has arisen as a Metacritic alternative. And unlike its popular counterpart, OpenCritic offers some degree of personalization for readers, allowing them to filter out the websites of their choice (hopefully not ours). The only downside can be found in the fact that OpenCritic also relies on review scores, though it does present them as they were originally published. My review for Her Story, for instance, is represented as a 4.5 out of 5 on OpenCritic, which Metacritic converts to a 90. And even sites that abstain from review scores, like Kotaku and Rock, Paper, Shotgun are included in OpenCritic's review roundup.
Even if OpenCritic somehow disrupts Metacritic's kung-fu grip on the industry, there's always the chance that its equivalent of the Metascore can be just as potentially destructive. Until then, though, it's always nice to have another option—just as long as you don't take it too seriously.