It's often an annoying cliche to compare 16-bit action RPGs to A Link to the Past, especially when lazy critics accuse the likes of Story of Thor and Soliel of being "Zelda-clones", when the only similarities are at the most superficial level. But in this case, there's a good point to be made, though it's done by contrasting this one with Nintendo's classic. The thing is, they're good examples of the differences in the design philosophies typical to their host consoles.
First off, there's the tone and aesthetic of each game: if ALttP can be likened to a fun, colourful adventure anime that gets dubbed on the cheap and aired at 6am, then King Colossus is more like a grim late 80s fantasy OAV that gets dubbed with extra swear words and released on tape by Manga Video. That is, while Zelda does have some dark elements, it's mainly bright and colourful, with the tone being skewed towards fun and adventure. In contrast, King Colossus has your orphaned hero being sold into slavery by the old man that raised him, being forced to fight to the death in an arena as part of a ritual honouring an evil god. (And that's just the start of your hardships).
The contrasts carry over into each game's structure, too: unlike ALttP, KC has no currency to accumulate, nor does it have a large open world to explore. It's a lot more linear and arcadey in its execution. Pretty much the entire game is spent in dungeons fighting monsters (or in the colosseum fighting your fellow captives), with only short expository interludes between them. There's still a little exploration to be done within the dungeons, but the meat of the game is combat. It's fortunat, then, that the combat is pretty good. There's an array of different weapons to find, and not only do the get stronger as you go through the game, but they also attack in different ways. There's swords, axes and spears that attack in front of the player at different lengths, as well as crossbows that shoot over long distances, flails that attack in a circle around the player and others.
The only criticism that can really be levelled towards King Colossus is that it is a little bit too easy. I'm most of the way through the game at the time of writing (and I do intend to eventually see it through to the end), and I've only died at two or three points in the game. Other than that, though, it's a fun action RPG that's a little darker in tone than the usual and it's worth a try if you're curious.