i find act 1 to be the best by far. everything is perfect, the setting, the layouts, the story and subsequent quests, the storytelling in the environment, the soundtrack (looking at you tristram and wilderness themes), the mini-bosses, the jail-cloister-cathedral-catacombs arc culminating with the andariel fight. perfection.
don't get me wrong, i love the other acts too, especially act 4, but none of them come close to act 1 in terms of atmosphere, worldbuilding and storytelling imo.
oh and of course, blood moor is in act 1
Couldn't have said it better myself.