Then where lies the difference between constructive criticism and complaining?
I can say, "Oh this shit sucks, I don't like this shit. Why don't you fix this shit?" but where would that leave the developer? Without the critic's input all the developer can do is go by their limited understanding of the audience's reaction and, in the end, fail to please anyone at all.
Good map feedback is rarely, "this area is overbalanced," it needs to describe why the area is unbalanced and in their reasoning, it will at least hint at a method of fixing it.
First of all, giving a description isn't the same as proposing a solution. I'd say most of the posts in this thread are describing an issue, and there's nothing wrong with that. My point is that giving your own solution won't help much. Chances are that your solution will be ignored and won't reflect what the developer wants. Even if you come up with a good fix, it might not have the same feel the developer was going for.
I trust my own decisions on my map, and I usually feel like I know what I'm doing. If somebody gives me a paintover of a layout change they want to see, I'll probably ignore most of it because I don't like it. It feels bad, since the other guy probably put a lot of thought into those changes, but I want my map play out the way I want it to. I'll bet most other people feel a similar way about this.
EDIT: Oh, and even if you aren't entirely descriptive about an issue, the developer should be able to deduct the source of the problem. For a new mapper descriptions help a lot, since they probably don't understand exactly why something is going wrong just by hearing about it. But for an experienced mapper, these things are usually pretty obvious.