Story: there are three factions you can join, each with its own storylines. So yes, it is somewhat story driven, but some players might prefer just exploring the areas and mostly ignore the story. Every storyline should last about 20h if you focus on that, 30-40 for a more "normal" playthrough without trying to do everything. I believe that a player who really digs the game and want to see everything and try every playstyle would take about 100h to do so.
The collectibles are not stuff you find in large useless quantities. There are some very rare items that can be gathered as a crafting material for some end game gear, but those are generally well hidden. Don't expect to find something in every corner, but if you don't look around you will certainly miss out on cool stuff.
There are 4 open regions of about 4 square kilometer each, each with very distinctive landmarks that often contain a dungeon to explore. Each region has its own flora, fauna and climate. There is a town for every region. Right from the start, you can leave one region and head wherever you want, with some dungeon areas sometimes barred until you have the relevant quest. During our latest stream, you can see what the world looks like and we've answered some questions about the lore of the area we were in.
There is a lot of fantasy elements. You can learn to cast magic, but that requires some sacrifice, and using magic isn't as simple as pressing a button to cast a fireball. The idea is to make an RPG in which you are not spoonfed supernatural greatness by a game that is always holding your hand. In that regard, we try to subvert many tropes, and we focus the story more on what other characters are doing in the world, and the player accompanies and assist them, rather than make the whole world revolve around you. It doesn't mean that the player isn't making any choice however, and sometimes with very intense consequences. Also, we try to have a story that isn't too simplistic with the good vs evil stuff, but some characters are certainly less likeable than others. Our characters have clear motives for their actions beyond "I'm evil, muhahaha".
As for the info being barebones on the store description, the point has been brought up a few times already and I agree. The publisher is handling the store page, not the devs, but I asked them to provide a bit more info.