[zooweemama]

I don't understand how this is legal or even just OK?

[larsiusprime]

Doom is open source. The assets must be purchased but are modular and easy to drop in to any compatible source port engine.

[wang_li]

The license was changed. You can't do that to other people's code. It was originally released under GPLv2 and he's changed all the copyright notices to say GPLv3. While the license included in the original doesn't bind the recipients to v2, recipients can't restrict successive recipients to a later version only. They have the option of v2.

[prurigro]

Doom is open source and I don't believe the author is shipping the copyrighted assets