I think there needs to be a protocol regarding giving feedback on custom packs.
Whilst feedback is useful, welcome, and encouraged, when unchecked it can also be quite harsh and put people off wanting to create custom content. I'm sure that there are many people who have thought about making a pack, but have seen the nature of some of the feedback that gets posted and have been put off.
Similarly, I am very sure that there are people who have removed content due to particularly negative feedback following an intense period of working on that content, leaving them feeling like their hard work and time was all for nothing.
As a basic suggestion, let's say you play a pack and there are several things you don't like about it. Before taking to the keyboard to type your frustrations straight away, take a moment to see if there's anything you do like about it, and then be sure to include that in the comments.
Ideally, each bit of negative feedback given should be balanced out with a piece of positive feedback. Praise is important: it keeps people motivated to try harder and put the extra effort in to improve their content. Simply listing a pack's drawbacks is only going to make the creator feel like a failure. Giving feedback is a powerful thing, and with great power comes great responsibility: use it wisely.
Suggestions to creators
ALWAYS get your pack playtested by at least 2 people, and be prepared to take a bit of harsh criticism initially - this will help you to shape your pack into its final product.
Then, when you release your finished pack, add a poll at the top. Something simple like:
What did you think of my pack?
1 It's excellent!
2 It's good, but some things could be improved
3 It's not really my cup of tea
4 I haven't played it yet
(Or even just a star-rating system from 1-5).
That way, you can get a good idea of what people who've downloaded your pack think, and it could help to balance out any negative feedback you get initially (unless of course everyone votes 3, in which case it's definitely worth having another look at it anyway!)
A poll would also encourage those who aren't predisposed to typing paragraph after paragraph of detailed feedback to leave something for you, for better or worse. That way, if a lot of people vote 1 or 2, but someone leaves a blazingly heated comment about how awful your pack is, at least you can see not everyone feels that way, and it'll be that much easier to take the criticism on board constructively, even if it wasn't necessarily presented to you that way.