The Deadly Rooms Of Death (DROD) games are some of the most challenging and entertaining puzzle games I've played on the PC.
Each game in the series is on sale at 50% off over the next four days @ game du jour:
Tue. May 26th: 50% off on http://www.gamedujour.com/5916-drod-rpg-tendrys-tale (DROD RPG: Tendry's Tale)
Wed. May 27th: 50% off on http://www.gamedujour.com/5918-drod-the-city-beneath (DROD: The City Beneath)
Thu. May 28th: 50% off on http://www.gamedujour.com/5920-drod-journey-to-rooted-hold (DROD: Journey to Rooted Hold)
Fri. May 29th: 50% off on http://www.gamedujour.com/5922-drod-king-dugans-dungeon (DROD: King Dugan's Dungeon)
They're well worth checking out if you're looking for something 'different'