Games are rated by a set of 10 criteria:
Each category is rated out of 10 possible points, and then totaled together to create a score out of 100. This is the final percentage score.
In most cases, remakes and remasters will replace the original game. There may be exceptions to this (the upcoming Resident Evil 4 being a case for this, since the “remake” also introduces new elements). Anything that introduces new gameplay and new areas will be rated as a completely new game.
The top 10 is scored a bit differently to present a clear and consistent separation of the best-of-the-best. The scoring is a sum of: