Iji is an excellent PC platformer made by Daniel Remar1. What intrigues me most about this game is the depth of game it provides, in both tactical combat and in the player's approach to the overall story.
Choices
One of the notable features of Iji is letting the player choose how violent they would like to play. While a similar mechanic is present in the well received (and much later released) Undertale, in my opinion, Iji's approach is superior. It better captures the seductive nature of violence, (it is easier to simply shoot enemies than avoid them carefully), and its vicious consequences, (with more enemies being dispatched for those on that choose a violent path). Perhaps most significantly, the choice to pursue a violent or peaceful path is never made explicit. Instead, it is completely determined by the player's normal actions during gameplay. These aspects make Iji a compelling meditation on violence.
Game Guide
A comprehensive game guide has been compiled by the developer. In addition to being a definitive walkthrough, it provides insight into the depth of the game. In particular, it outlines the many secrets that are peppered throughout the game, from hidden weapons to fiendishly difficult to reach areas. My favorite secret is the epistolary love story that takes place in the background, which I would not have noticed without the guide.
Open Source
Sources for Iji are available on the resources page. However, since the game was developed in Game Maker, one must have Game Maker in order to compile it. Fortunately, the game works well with the Wine emulation layer, and so is playable on Linux.