I found Diablo 2 immensely boring to begin with, never could stand that game. However I did not find it at all disturbing in Diablo 1.
Tbh it only becomes disturbing when you fail at the area randomization and make people feel that you are running through same area again and again. Diablo 3 is very bad at this so that could be considered as aspect to cause the boredom as well.
"Oh look, I go through this exactly same shaped area again and again but it doesn't matter because those two trees switched places"
It didn't help that their overall area art was 100% identical within entire zone, except for Act II which had all sorts of cool different looking desert zones and lush zones and palace zones and city zones.