Can someone give me a quick tldr why everyone is losing their mind over this?
I don't know anything about this game or it's predecessors.
Is it just a fantasy RPG or what's the hype all about?
How is it different from other fantasy RPGs?
In Diablo side quests do require you to ask how you can help and then you get the marker, so that sounds fairly similar. Is Baldurs Gate a main story and then an endless set of side quests?
Side quests in Diablo and bg3 are vaaaaastly different. They're much more like Skyrim but that still hardly does it justice. In Diablo you find a burning building then the survivor says you need to find her sister in a different unrelated dungeon and you get a nice quest marker directing you there. In bg3 you find a burning building and if you make a skill check you might save the last survivor, then you can extort them for money or just kill them if you really want, then they mention their sister is trapped, you can ignore it or promise help or promise more of a reward, then you get a journal entry describing where you're currently at in that quest and it's up to you how you handle it from there.
Not to mention sometimes there's no quest markers. You see some npc steal from some other npc. it's not a cutscene or anything, you just happen to be watching the NPCs do their thing. So you decide to go talk to the thief. You can either let them go, tell on them, fight them, extort them, or extort them and tell on them anyway.
And nobody in this thread has even talked about how much animals know about what's happening in the world when you talk to them.