I’m thinking 2015 - Witcher 3, Undertale, and Kerbal Space Program are all classics. Fallout 4, Arkham Knight, and Cities Skylines were all excellent too, though fallout 4 and Arkham knight aren’t necessarily the best games in their respective series.
Maybe a hot take but I think this year has been one of the best for gaming in a long time. We got Claire obscur, kcd2, Hades 2, silksong so far