Wolfenstein 3D is the ur-FPS. Undoubtedly a landmark technological development in the history of digital game design, but, to be honest, will not necessarily hold the same appeal twenty-eight years after release, especially not among those without at least some degree of nostalgia for the franchise.
If you do want to play it, for the first time or otherwise, and want an official copy, Steam does have it. Although, the program available from the store page is literally just the original sixty level non-shareware package running in an instance of the DOSBox emulator. Very little is available in terms of resolution fixes, sound card support, and so forth that you wouldn’t get better assistance with from a copy from any retro game roms website and a fan-patch.
The game itself is still a classic if you can handle the tanky 1992 controls and minimal depth on top of what is essentially a not-particularly-challenging maze that just barely meets the technical definition of “3D”.
Don’t go in expecting a 10/10 shooter experience, but keep in mind that Wolf3D codified the FPS genre for a reason.
And you can’t tell me Mecha-Hitler isn’t one of gaming’s most inspired boss designs.