Reviews and ratings
Unlike western countries, the way people use reviews and ratings tends to be a bit different in Japan. Also, the popular apps and services used for reviews are different.
The largest and best restaurant review service in Japan is called Tabelog, literally "Eat" + log. It's highly recommended to use. Overall, Japanese reviewers (such as on tabelog) tend to be more strict or harsh in their evaluation of businesses.
Japanese consumer's food standards are very high. Taste preferences are of course different from westerners as well.
Out of five stars, three stars are often used when the place is solid or "Good"
Ex: A place with 3.1 or 3.2 stars
Four or more stars are only used when the place is really "great" or truly "exceptional."
These places are probably going to be very popular and require advance reservations or careful timing.
Even some higher percent two star places may be quite good actually!
Ex: 2.7, 2.8 star places can be good choices.
In general, Google Maps reviews and ratings lean towards tourists and the ratings tend to be a bit higher overall, more similar to how we might see reviews in USA, etc. where 3.5+ stars is a baseline for good options. Accordingly, Google Maps results may have limited accuracy but can still be used to get a general sense.
If a place has lots of reviews and a very high rating, it's still going to be good, and the reverse is also true.
Note: Yelp is not very popular in Japan. 増井俊之.icon
I think the above problems described by ben.icon only applies to Tabelog, which has bad reputations. So it is not the problem of Japanese people and rating systems of Japan. It is just the problem of Tabelog. Don't trust Tabelog, and that's it.