I do wonder whether it's a slight failing in the game design, however, to allow the player to succeed with such a poor performance of the required task.
Also, I don't think it's entirely fair to criticise all reviewers for picking up on this aspect of the game, especially as for many people the only reason to play games is to get to the end.
Sometimes the intended objectives can be failed almost completely so long as your time is good, if you're only pushing to unlock everything. I do feel that players would enjoy the game more if they had to do better at stages, but I can see why this might be annoying for players that get stuck on certain stages.
It helps that I came into this game knowing about the 'limited' amount of content, however, so I've been avoiding playing and unlocking missions until I've done at least 2 stars on everything beforehand.
People are always critical of Mii based games too. Wii Sports Resort is amazing, but gets dismissed curtly and quickly by many people. I would have to have seen some of the content seen in Wii Sports Resort (such as multiplayer/dogfighting) and even the Chicken Suit from Wii Fit Plus. There's plenty to criticise for this game with regards to falling well short of its potential, but such is the difficulty of launch titles.
Oh, and ghosts and leaderboards for competitive play would obviously be amazing. I hope Pilotwings is a success, I'd love to see this game expanded upon.