However, we were pleasantly surprised at how good it was and played it a ton.

That’s because it’s a licensed mod of Doom. Literally, the first level was just the first level of Doom reskinned. I replayed it a few years back, along with 2 and 3 (3 includes a remaster of 1 & 2), and it holds up pretty well.

Don’t you still need to use the Steam client to install those games? I’ve never seen an option on the website to download the game files directly like GOG does.