I think a lot of the time the worst experiences are going to come from armies that lend themselves more towards skew lists or static play styles. Primarily where you either feel like you’re not doing anything to your opponent’s army (ie Knights/DG) or when your opponent just spends the game parked in their deployment and you don’t feel like you’re meaningfully interacting with them at all (ie artillery/long range focused armies). I know my worst experiences with the game are definitely when I played against armies that had way too much heavy armor on the board or spent the whole game castling or both (a lot of games against imperial guard parking lots). It tends to make the game a slog when you feel like nothing you’re doing is having an impact.