It's time to give each other's games a try! If you haven't already, find your most awesome game in progress, your work that you'd like to see be a famous game someday, but perhaps it's still a diamond in the rough, and brace yourself for all the, um, nicest possibly said things people will say about it!
Then, go play everyone else's game! Tell them what you thought about it!
Sometimes it's hard to give useful feedback. Sometimes, all you can come up with is, "this isn't fun". But try to tell more. Is it the graphics? Is it the controls? Does the purpose of the game feel futile, or not important enough?
Sometimes, it feels hard to give useful feedback without inadverdantly hurting the person recieving the feedback. We are all going on a limb posting our games here, saying "try this and tell me what you think". Please refrain from simple comments like "this sucks". There isn't much there to be able to improve our game from.
Sometimes game authors take the feedback and immediately implement it, before Feedback Fortnight is finished! Watch the comments of games you've already played, perhaps the author has already implemented your feedback!
Although those small thoughts aren't the entirety of things I could say about giving feedback, in the interest of keeping the post small, I'll stop here. If I haven't said something you think is important, please leave a comment here! In the meantime, go here and try out all the games!