Did you have fun? is useless. I have given the unhappy face just to get the same issue the following game that made me unhappy in the previous. If this feature is just a click something to make yourself feel better, remove it. If it is actually there for game improvement, adjust it so it can be an improvement tool. I suggest having a multiple choice for those who choose unhappy. I suggest the following is asked when someone chooses unhappy:
1) dislike the deck matchup. After extensive recent playing, I am tired of seeing the same 3 decks. Use this as an option to make better matchups and reduce early concedes. I regularly concede as soon as I see certain decks such as red/white energy, omni-tell, Thassa, Goblin charbelcher, heist or black decks that involve overplayed, broken cards (grief, orcish bowmaster, turn 1 discard like thoughtsieze). Decks that are no fun to play against.
2) poor shuffling. I have many times mullianned 3-4 times to try to find a card concept I have 8 of in my deck. If you do the probability math, I should find that card on one of the draws.
3) bad draws. I have tied to work with a questionable hand after a few mulligans. Usually, if I do not draw a card I need if I roll the dice for percentages. If I need a land with playing 33% land, I won't see one for the next 5 turns. If I am looking for a spell, I WILL draw land for the next 5 turns.
4) poor land draws. In my 60-card deck that has 20 lands, needing one each of 2 different colors to work, I regularly get mana screwed. I started with 4 pseudo dual land and 8 of each basic. I would consistently only draw one color. I have since used a bunch of wild cards to get a more consistent draw. Now with 12 pseudo dual lands and 4 of the 2 basics, I still see draws of only 1 color.
5) Ropers. opponents that just run out the timer hoping you will concede instead of conceding themselves when losing or just taking the loss.
6) other. If there is another reason the player was unhappy. This should allow for a comment or what the reason is.
This option should also be available after every game, not just sporadically. I have seen it pop up twice within 5 games and also not pop up over 20 games.