This is one of, if not *the* best puzzle platformer I have ever played.
First, the concept is a novel one. I can't think of any harpoon-based games, and yet it is executed as if the genre had already been solidly established. The use of moving projectiles as part of the level structure indicates a clever and keen sense of level design. Droqen does not insult the player's intelligence by putting the most basic of handholding tutorials in. Instead, he lets the player discover what the implications of her actions are as she plays and expects the player to think instead of just letting her eyes gloss over as if playing a run-of-the-mill uninspired platformer.
Second, the graphics are simplistic, yet convey everything the player needs to know. The pixelated graphics actually contribute to the design, since the bigger pixels allow better precision in movement (which is needed!). If there's one non-aesthetically-related thing that big pixels do, it's clarifying where the player can and can't go and what she can and can't do. Hand-drawn graphics may be argued to be more beautiful, but it's almost always unclear when and where a character will fall off a platform.
The controls are tight, the music is engaging, and the game offers extra challenges if the player wants them. Honestly, Fishbane is exemplary of practically everything I enjoy about gaming.