I fully recommend Qbeh-1: The Atlas Cube - it's been a long time since I've been that obsessed with carrying on in a game.
"First person 3D platform discovery puzzler" is how I'd sum up the game category. As such, the game is to some extent comparable to Antichamber and Portal, both of which I have been playing in recent months. There is even a reference to Portal hidden in one of the Qbeh-1 levels.
Despite Portal and Antichamber having more innovative game principles, of the three I enjoyed Qbeh-1 most.
As I see it, the beauty of Qbeh-1 stems from the level design, the atmosphere and ambience. It has the feel of discovering abandoned places of ancient cultures, with some left-over machinery such as doors to be opened with switch mechanisms, cube elevators and fans (ventilators). The background music perfectly enhances the visual impressions and the "exploration" feeling. It will change at some points within levels, for example upon entering impressive, awe-inspiring halls.
Qbeh-1 is linear in the sense that there is one level after another, each a place of its own, with its own theme, and separate from other levels.
What may seem odd at first, but really adds a lot to the atmosphere, is the fact that each individual level is located mid-air, sort of "in the clouds". You will often find yourself balancing on the brink of "abyss", and falling down is the main danger to be faced in many levels of the game. Due to cleverly placed checkpoints the game never feels frustrating. Many of the places feel like ruins, some of them crumbling under your feet.
Discovery is one of the main joys in the game: There are several surprises to be found within the levels, and finding special items hidden within the levels is part of what's needed to beat the game. So looking around closely to find non-obvious paths to progress on is essential in Qbeh-1. Often you'll find yourself "outdoors", or peeking outside hallways and halls, getting the tease of seeing parts of levels you want to progress to, and not knowing yet how to get there.
Your basic interaction with the world around you consists of running around and jumping, similar to most first person 3D games. Most other interactions are done by collecting cubes - there are different types scattered in the levels - and applying them in certain locations within the levels, sometimes to activate switches, sometimes to build bridges or to provide other means of getting to some place that would be unreachable without cubes. These "cube application puzzles" will rarely be intellectual challenges to spend hours on. However, there are often different ways of applying the cubes - it is a creative task with non-obvious solutions and surprising new paths.
Usually you have all the time in the world within the levels. There are only a few locations and challenges within the levels, such as elevator cubes and fans, where accurately timed jumps and cube placings are essential.
It feels really rewarding to reach parts of levels previously unreachable, often seeing levels from completely new angles, and often climbing incredible heights - face your vertigo!