amazing game
Gameplay: really good gameplay, a nice mix of puzzles and action. There's lots of variety in the action - sometimes you'll be fighting, sometimes solving puzzles, jumping gaps, swimming past enemies, dodging traps and more.
Graphics: the graphics are amazing, it's 2006 and they still look good. The resolution is just plain awful, even in the FMVs, but this can't stop the brilliant art design from shining through. Every character and environment looks great. While most sidescrollers repeat their background sprites over and over, Heart of Darkness has almost no repitition in backgrounds. The graphics are brilliant.
sound: the music is mostly good, especially the main theme. The voice acting is excellent, especially the idiotic flying friend Amigo. Sly chuckles from the shadow-like enemies and other environmental noises round out the package.
value: the game is fairly short, but it's good value in as much as you won't feel ripped off when it finishes. The short length actually helps the brilliant story, because the writers didn't have to cram huge amounts of gameplay between each plot point.
This game is awesome, it has fairly simple but fun gameplay set against a background of presentation which is unmatched except by the most brilliant of titles.