There is a very good reason why designers tend not to explain the specific details of design "suckage" but simply exclaim "it sucks." "It sucks" means that the design has to be thrown out, and one should generally start from scratch. What you're looking for, on the other hand, is an explanation that goes something like this "ok, this part of your design is pretty good, but this one is the really sucky part, and it is sucky because you did so and so, and you only need to change this to so and so and you're good." What you're looking for, in other words, is way to incrementally improve upon an existing design, which is the way engineering and software development is often done. Designers don't think like this. Designers frown upon incremental improvement, since it would imply (1) That design rules are being codified -- which is first of all hard since language used to describe the emotional associations this or that design evokes simply may not exist, and second of all may not be desirable since codification often means banalisation; (2) That design is not holistic -- which means it has some similarity to the dreaded case of a design by a committee ("ok, you do this part, I will do this part, and she will work on that part"), the end result of which is, as we all know, a camel, not a horse.
The best design is always holistic, which means that (1) one and only one person either completely designs everything or closely supervises the entire process, and (2) it is impossible to redesign any single part of the product without redesigning most if not all of the other remaining parts.
Therefore, in design, it is either "it sucks balls; start over" or "this is groovy; rock on."