I mean I was able to finish Dark Souls 3, but I didn't with Dark Souls 1 or 2. Maybe it is the shorter game, but it definitely has less unpleasant and unfair surprises in their boss mechanics. And I loved O&S.

Nito's respawning enemy crowds, Seath's forced death and 4 Kings basically being a dps fest is honestly more or less bull**** boss design.