What are some alternatives?
When comparing Team Fortress 2 and Doom, you can also consider the following products
Overwatch - Stylized team-based FPS
Quake - Quake is a series of first-person shooter video games released by id Software.
Warframe - Ninjas Play Free.
Xonotic - Xonotic is a free (GPL), fast-paced first-person shooter that works on Windows, OS X and Linux.
Arma - Experience true combat gameplay in a massive military sandbox.
Call of Duty - Call of Duty is a first-person and third-person shooter series by Infinity Ward.