A review after one hour is not going to be sufficiently in depth, however, in very many cases, one hour would be enough to give an informed opinion. Jim Sterling has an entire series on playing games for less than an hour [https://www.youtube.com/playlist?list=PLlRceUcRZcK0zAt8sV33ZsMCVlOgWjVoy] - sort of an early impressions of games and a lot of the videos are up to 20 minutes long. In the majority of cases, there is really not much need for more than that. If you look through the user reviews in steam, often you can find a very helpful review from a user who has played no more than an hour.
Sure, not all games can be sufficiently summed up by the first hour, however, there are lots that can. Bad games, in particular, require very little time. Other games do require more investment but even then a lot of times you can determine whether you'd like to play more or not in an hour. Again, there are exceptions to even that - "slow burn" games that require even more time investment to truly be grasped, however, that's not actually that many of the games in total.