Portal 1 Test Chambers (Evolution)
From Valve Cut Content
Most of the work done on Portal was refining the artstyle over it's 2 year development.
Version 1: Nova Prospekt (2005)
The first iteration of Portal's art style is the "Nova Prospekt" theme. Early on Portal took design cues from Half-Life 2, including using mostly HL2 assets. Test chambers during this era largely resembled the Prison/Nova Prospekt levels from HL2. The style included a mix of Combine architecture and steampunk technology. Chambers have a very "block-like" look to them aswell as most puzzle elements being made as brush work.
This article about evolution of a subject could be expanded.
