According to MetaScore data (which ain't perfect, but still a good indicator for trends), 2015 was a solid year for PC games:
- http://www.metacritic.com/browse/games/score/metascore/year/pc/all?year_selected=2015&sort=desc
- http://gamrconnect.vgchartz.com/post.php?id=7692982
Most 90+ PC games since 2008 (7 games, on par with PS4), only 2002 and 2004 had more PC games with 90% or higher (although I can see "Nuclear Throne" fall under 90%).
Most 85+ PC games since... ever (35 games, second place is PS4 with 26 games with 85% or higher). Best "85+ years" before: 2013 (34 games) and 2000 (30 games).
Most 80+ PC games since... ever (91 games, second place is PS4 with 71 games with 80% or higher). Best "80+ years" before: 2014 (91 games) and 2013 (81 games).
Most 75+ PC games since... ever (168 games, second place is PS4 with 117 games with 75% or higher). Best "75+ years" before: 2014 (148 games) and 2013 (145 games).
Essay Pro