I usually average about 100hrs for open-world games that I enjoy. Somehow it's always extremely close to 100, give or take 10 hours, and depending on DLC.
Few games that fit this bill:
-Witcher 3
-Fallout NV and Fallout 4
-Skyrim
Other games that I play in Single player, amassing over 100hours
-Rainbow 6 Vegas 2 (probably 300hr or more, love challenging myself in different scenarios, clearing maps with just pistol, Realistic Difficulty, High enemy density)
-Assetto Corsa (didn't even complete the career mode, just love drifting touge maps and hotlapping the Nurburgring, modding community is the best)
There'll be more for sure, this just the top of my head