You named also a few arcade games, which I don't really count as C64 games, as they just were ported to other computers/consoles.

Spindizzy was a great game, and very tough to play through, and guess what, the ending is one of the crappiest ever seen, once you have collected the final jewel, a message appears, which says, "YOU HAVE COMPLETED 100% of screens, 100% of jewels, 100% of game. SURVEY COMPLETE". That's it?

It was a platform game where you started at the top of the level and had to drop down into cave systems.
I immediately thought of Hero, but when reading further, it isn't Hero.