[waru]

What if you tell them one specific thing to work on (whatever their major downfall was), and then be vague about the rest? Then, even if they insist that that one problem area was actually good, you can point to the part that vaguely says something like "Though your game is not a suitable match to our site for a few reasons, [we suggest you work on blah blah blah]..."

I don't have any experience with rejecting people in this situation, but I know it would be nice as a developer to have something to try to improve after a failure/rejection.