Below, we can see a chart of the top 20 players in the Premier League in 2015/16 based on their expected goal contribution (expected non-penalty goals plus expected goals assisted) per 90 minutes.
Keen eyes will observe the noticeable lack of Riyad Mahrez, who was one of the keys to Leicester's title win in this season. The reason is that Mahrez had one of the best overperforming of xG that I have ever seen. He scored 17 goals from 7.462813xG, with a ratio of 2.28 goals/xG. In the top four leagues in 2015/16, apart from those with less than 6.0 xG, nobody had a better goal/xG ratio than Mahrez. For context, in 2012/13, Messi had one of his best seasons, scoring 42 goals from 17.6xG with a 2.39 goal/xG, only slightly edging out Mahrez.
All data from StatsBomb.