Shadowfire can be seen as a revolution in the big adventure market on C64. Back in 1984 adventure meant "text adventure" and icons were simply future. Even if it was a gaming experience very complicated by an icon-drive interface, after you understood the simple rules of inputing orders to your team, Shadowfire gave its best.
As I said, it has some flaws: icons are not so easy to understand, and if you don't read instructions you won't be able to play it all. Plot is a very easy: you need to give orders to a group of superheroes to rescue a man from a space base. Even so, Shadowfire is a game that still needs to be played even in 2012: its music, written by Fred Gray, is one of the best C64 tunes and the dynamics of the game are still satisfying today.
In the original tape, there was the C64 on a side and the Spectrum conversion on the other one, but the C64 featured a great soundtrack.