TSP isn't really about liminal space, it's about narrative decision making and the consequences of trying to account and develop for that in video games. I suppose you could say that it uses the liminal space of a barren office to achieve an awkward atmosphere that is meant to make you question everything about it, but that's a really small aspect of the game as a whole.
If we're going there, we may as well mention Portal which predates Stanley Parable by 6 years, and features liminal spaces with the same eerie feel - in the game, you wake up trapped in an abandoned laboratory that seems to go on forever, which on its own hits the liminal notes a bit, and then you suddenly find yourself breaking out into service corridors and navigating the backrooms of the facility. Portal 2 (two years before TSP) continues that theme, though I feel it overdid the scale a bit, to the point of breaking suspension of disbelief.
Portal and especially Portal 2 have a very different feel to them for me - too dilapidated to evoke the same feelings as the office maze in TSP. There is also that TSP goes for retro while Portal goes for retro-futuristic.
