The name is familiar, but I don't actually have any copies of it. It would be good to add Japanese sources to the gaming articles to expand their reception sections because the inclusion of sources from different nationalities helps to reduce systemic bias and POV. Naturally English Wikipedia will use mostly English-language sources, and naturally there are a lot of high-quality English-language RSes, and these are sufficient to demonstrate a game's notability, etc., but high-quality or major non-English and multinational sources would address Wikipedia's second pillar by reducing or eliminating cultural biases in the reporting. It sounds to me like reviews from GAMEST would be a great addition to Wikipedia for this reason.
For articles on games created in non-English-language countries, I think it's also very helpful for a full grasp of the topic to include reception from the originating culture. So in my view, reviews from Japanese sources like Famitsu or GAMEST should be used to expand the articles on Japanese games whenever possible. (And similarly, reviews from French magazines would be helpful for French games, and Russian magazines for Russian games, etc.). I have heard that Famitsu is considered Japan's premier video game magazine so I think that its reviews for Japanese games are particularly helpful, and I have been adding them to gaming articles recently, but thanks for bringing my attention to GAMEST too. If I happen to pick up any copies of it I'll try to add reviews from there as well. Cheers, -