What is it?
Constructive criticism is being able to process and offer your own thoughts and opinions in order to give courteous and friendly feedback. This is done by explaining what you like and dislike, while at the same time providing feedback that is useful. This is what separates constructive feedback from ranting/complaining and flaming.
Does it help? How?
Yes! Constructive criticism helps because not only are you giving feedback about what you don't like about a quest/event, but you're also giving feedback about what you DID like in the quest. Feedback could include on such topics as statistics, more dialogue, more explanatory cutscenes, more fights - everything that quests or events would normally include. This gives the game staff a better idea on future improvements.
Example of Constructive Criticism:
"I didn't partularly like this war because it felt too empty. To have made it better, I think the staff could have had a 50% cutscene to unlock rather than just a shop to progress the storyline. As it was, I personally was a little dissapointed that this war felt more rushed than previous wars, however I do understand that the staff had a lot on their plate when making this release.
That said, I greatly enjoyed the boss fight, the animations and art fit perfectly with the song that was playing in the background. So while not one of the best wars DF have done, I still enjoyed it. Thank you, DF staff!"
Example of Unconstructive Criticism:
"I didn't like this war at all. What were the staff thinking? The items in the shop were ugly, overpriced and were bugged!! No cutscene? That was never done before and it is not how it should be done ever. Seriously, doesn't the staff ever listen to us?! The boss fight was too hard and took forever to beat :( And there was no sound. I dont think the staff even care anymore. Best war ever /sarcasm I hate this game D:<!"