Mate if you are complaining about graphics than you are talking about the wrong series. Aside from the ascetics the only other complaint you have is about the ai which if I'm not mistaken is pretty stock standard these days. Fallout has always taken gameplay over graphics.
The story is a storey of the world. Each game is pretty much self contained however they are all in the same world. I don't think that there is a story from one game to another aside from 1 and 2 which i haven't played. To be honest i don't think it matters what order you play it in. I played New Vegas before 3 and it didn't really matter. Edit: Unless you want to play an isometric turn based game skip 1 and 2. Number 3 is the first open world game.