In my opinion, yes. On the other hand, I have been using KOReader for many years. When I started using it, it was very rough. At one point there was a fairly significant overhaul. Since then, there have been smaller incremental changes (which amount to a lot across the years). Of course, opinions of user interfaces will vary.

I am not going to claim that it is perfect. They cram a lot of functionality in there that serves a very diverse audience. The volume of options is going to have a negative impact is going to have a negative impact for anyone wanting a simple, to-the-point interface. The diverse audience bit means that virtually noone is going to be interested in a majority of the features, even though I suspect that a majority of users will interested in a combination of features that they won't find in other products.

While I may have been a bit unfair in saying that most commerical reading software is geared towards selling novels, I don't think that assessment is too far off base. Most software does appear to be designed for people who just read novels. KOReader is geared towards people who care about features that other reading software rarely provides.