The fact that Leia loses her planet is extremely under used in her characterization. For ANH, that's okay or whatever, because it's a standalone fantasy fun adventure film. We don't want a moping Princess being saved. But still. In ESB, there is no mention, same with ROTJ. Unfortunate. (On a similar note some people criticize Luke's lack of reaction to his family's death, but I think the fact that it provokes him to join the rebellion is about enough.)

There are also a large number of character and story problems with ROTJ, but these have been discussed at length.

As well, the acting isn't perfect. I have arguments with my friends often about what is the best film trilogy and I always say the OT, but I always have to concede acting to stuff like LOTR, The Godfather, The Dark Knight, etc.