"THAT" is a single player source mod that runs on the 2007 SDK engine. It is more of an art installation than it is an actual game, it is my also one of my personal endeavors to push the "games as art" movement which I strongly believe in. The game features abstract surreal scenery and doesn't really contain an objective, it is more of a game to relax to and explore. The game is set in a grid of 9 maps, starting in the center (5th map). You can travel between the maps at your own leisure. I hope you enjoy it and that it encourages game designers to think outside the box when it comes to creating games.
First off I just want to say that I really enjoyed the aesthetic of this game. The vivid use of colors and the primitive geometry really sucks you in. The theme of kind of following the evolution of humans from jungles and swamps to Egyptian and Roman times and finally to space and heaven (at least I think that was supposed to be heaven) was an interesting progression as well. The music nicely complements all the above elements.
Where I had a problem with this game is that everything feels very static. I understand this game focuses almost entirely on exploration, but as it stands now it feels like walking through a digital statue garden. Not much really responds to the player. I'm not saying the game needs objectives or enemies or anything like that, just someway of acknowledging the players presence. It could be as simple as having birds fly away when you get close, or people moving out of the players way. The cubes were a nice way to incentivize exploration, but other than that there is a major lack of interactivity.
A similar game that does this very well is Proteus. It's very similar in that it has very basic visuals and a strong focus on exploration, but has multiple ways that the player can interact and change the world the player is exploring.
Other than that there were a few technical issues, with models appearing where they shouldn't, and the transitions between each level could have been smoother. But, overall I feel that the game was successful in what it set out to accomplish. I'll be interested in seeing what you do with TRIP.