Pilotwings is a solid game - it looks good, controls well, and accomplishes exactly what it sets out to do... but unfortunately it held virtually no appeal for me after the first hour. In fact I got considerably more play time out of Steel Diver. Not sure why things didn't click, but the game just felt "too niche" for me to recommend to others. If you see a copy on sale it's definitely worth a shot.
True enough, it is somewhat of a niche game. If all you care about is completing the missions, and you don't give a crap about getting 3 stars (or even perfects) then I could see the fun factor go down significantly. A huge part of the thrill in Pilotwings is in wanting to get those high scores, playing levels over and over again, and feeling a great sense of accomplishment after honing your skills and being able to do something that seemed impossible at first blush. It's the same thing as with Might Switch Force, another game where if you don't care about getting the par times, then I'd imagine the game wouldn't be much fun (and would be very short).
If you think about it, it's a really interesting design problem, where the game is designed for you to be able to play it and progress in it without caring about high scores/ratings, but then, if you do play it that way, then your overall enjoyment of the game is soured. But I can't think of a good solution, really. I heard a lot of people complain about Ghost Recon because it had so many objectives that, if you failed, required you to restart the mission or go to an old save. Especially if you lost the Russian girl, or lost all the Russian soldiers, and the AI seemed to know that because whenever the Russian girl was with you, the AI always targeted her first.