It sucks that you feel that way. I recommend the graphic novel Darth Vader and the Lost Command. There's also an ongoing limited series, Darth Vader and the Ghost Prison that I think is pretty good as well. Both of these stories take place between ROTS and ANH. Actually the Agent of the Empire and the Dark Times series, which also take place between ROTS and ANH, are both good too. I also recommend the comic series Knights of the Old Republic. Though it's set thousands of years before the films I think it captures the spirit of the original films pretty well, though I don't think any of the villains are as compelling as Palpatine or Vader, which of course is a tall order.