Bringing in the retro homage of pixellated platform gaming, Stealth Bastard is as treacherously well designed as it is visually enticing, and the pricetag isn't so bad either (it's free).
The game, designed by Curve studios, is of a simple premise with a rather high difficulty level. A multitude of levels greet you into the core mechanic of a blend between your average platformer and 2d stealth action game, so far so good. After completion is when things begin to get interesting, as a fully-fledged level editor becomes open to you, and a whole community of shared levels becomes accessible (hello Little Big Planet). All of this heightens what is an extremely tempting proposition with remarkable value for money...in the way that you don't pay anything.
Downside? Windows only, Mac people will have to wait.