Why are we here? What is our purpose in the universe? Why didn't Darth Vader recognize C-3PO and R2D2? These are the big questions of our time, and they demand to be answered. Now, with a franchise as massive as Star Wars, we almost expect to get a certain amount of plot holes, but that doesn't make them any less baffling.
The unanswered questions from Star Wars are compounded by the fact the series was released out of chronological order. The original trilogy dealt with the middle part of the story, while the prequels were written two decades later. This obviously led to some problems for George Lucas, as he fleshed out story ideas and changed particular plot points to better suit his vision. He also had to incorporate some foreshadowing into the Star Wars prequels, which inevitably led to narrative confusion.
Telling the story in such an unusual way was always going to result in some inconsistencies in the Star Wars movies. And while some of these have been addressed in the expanded universe, most fans are only aware of the plot points that take place in the actual films. Unfortunately, that means there are still plenty of plot holes in Star Wars that continue to bamboozle even diehard fans.