I spent a month recreating an iconic opening video game level, Point Insertion, from Half Life 2. I wanted to make it completely playable - which was a challenge, given the scale! But I worked smart on this one, pretty much exclusively using trim sheets for everything, and kitbashing/reusing assets heavily. I relied on prefabs a lot too.
Credit to Valve for: the citizen, civil protection, scanner, and Combine light models. I upres'd them through adding additional geometry, and updating the textures. Also, for the audio, which I used to try and stay as true to the impeccable atmosphere they created in the original game.
The rest of the materials and assets are made by me, with the exception of: some Megascan boxes and decals, which I also modified to fit my project. Also, the train, which is an asset I bought but heavily modified (I'd say probably 80% of it is completely changed from the original) in terms of its geometry to work not only with my trim-sheet workflow, but also to reduce its density. I created a brand new interior as well.