Well, this really depends on the platform. If a game is on Steam, obscure might be defined by having less than 1,000 reviews. If on Itch.io, obscure might be less than 60 ratings or a full page of comments. If on a console, it may be less than 250,000 copies sold. If the game was sold on multiple platforms, then the amount of "obscurity" is defined by all of these factors minus 10% for each, in case of repeat consumers.
To quantify:
| Steam Review Count | Itch.io Ratings Count | Console Copies Sold | Total Obscurity |
|---|---|---|---|
| > 1,000 | > 60 | > 250,000 | 1% ‑ 50% |
| < 1,000 | < 60 | < 250,000 | 50% ‑ 100% |
| 1,000 | 60 | 250,000 | 50% |
These are only general guidelines used to make sure it is fair. There will also be other considerations, such as how much people are talking about the game and to what degree. I do not intend to make this a hugely scientific affair.