I've played both Pathfinder games and enjoyed it.
But this Warhammer 40K setting isn't very appealing to me. And the alpha demo shown by youtubers didn't show anything enticing to me... It looks like most of the time we're in those industrial environments (lots of metal and boxes). The lore looks like more complex and yet, less interesting. I know this setting has a bazillion of books, so I guess it will be more difficult to get into (I didn't have any previous knowledge of Pathfinder, but the story and the hyperlinked hilighted words that allowed a popup to explain the lore, was more than enough to get to know the world and its lore).
I hope they manage to find a way to ease us in into this world.