How is the story (and characters) though? Is it any good or just an extra bonus with the main focus on gameplay exploration?
Story is meh, it's basically a guideline to help you progress through the open world. Characters, kinda depends, a lot are forgettable, some are pretty ok, but they're very cookie cutter medieval fantasy stuff.
Game's definitely not about this aspect. There's a barebones romancing system, there's some questchains that delve a bit deeper into the characters and some side quests specifically for them to raise your affiinity, but it's mostly all just there as some sort of filler, a box that's ticked really. It's not like Dark Souls where a lot of stuff is implied and you have to look for the story by yourself, and it's not like Dragon Age or Witcher with that massive storyline with tons of characters and you're always doing something in relation to the story and doing quests and stuff.
The game is mostly about exploring a fairly open world(there's a few things locked but not that much, at least once you've completed the starting area), fighting things, becoming more and more powerful to fight more and more powerful enemies. It's very action oriented. There's no puzzles and stuff either, it's all very straightforward. Then the expansion just didn't even bother with the story bits, it has Dark Souls-like storytelling but with no lore anywhere, so it's just basically a large dungeon with strong monsters. And that's fine I think, cause the combat is fun and engaging.