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.
It think it has to be 2007 just because there are games that didn’t crack the top 10 that year that would be goty in other years. It’s also a huge year for multiple platforms, pratically every major franchise had a good release that year.