The numbers here are surprisingly modest, but then again, the people who really dedicate themselves to a single game mostly hang out in the respective community and not so much on NeoGAF.
1. BotW (310)
2. Splatoon 2 (90)
3. Factorio, probably: my time on Steam is closing in on 300, but most of it was in 2016, and I think I put in about 70 additional hours this year.
I don't have numbers for StarCraft II and Heroes of the Storm, but would estimate they are also comfortably north of 50 in 2017. Arms and Fire Emblem Fates are also around the 50 mark.