So this really is just a Clannad bashing thread. ...Let me get in on this too.
My problem isn't that it has a happy ending though (because I'm a sucker for cheesy happy endings) but that it is painfully abrupt and does not properly explain anything. If you're going to essentially overwrite everything that happened the last few hours you could at least have the decency to make it longer than it takes for me to finish my breakfast.
Speaking of Key, Little Buster's ending also felt like chickening out. Maeda, If you want your happy endings, which again I have no problems with, properly set them up. Not these rushed Deux ex machina things.
Honorable Mention also goes to VA-11 HALL-A for kinda just ending. Didn't even realize we were near the end until I got the Thank You mail. Felt like the author either ran out of inspiration or time.
I wanted to go into more detail but it seems I can't get the spoiler function to work on my phone at the moment. Oh well, considering how popular these threads tend to get you won't have a shorthand of people telling you why your favorite ending sucks