This was made in the same game engine as Wolfenstein 3D, but with a huge number of improvements like floor and ceiling textures, one-way doors, power barriers, explosions with splash damage, and enemies that fake death. Stealth is actually possible using the silenced pistol in some situations.

Also, none of the pushwall secrets can be broken like they were in Wolf3D if you push them from the wrong direction.

This is a really good early FPS, although it was outclassed immediately as Doom was released exactly one week later.

There's also a great source port written by a Ukrainian gentleman: http://bibendovsky.github.io/bstone/

Definitely worth your time if you liked Wolfenstein 3D.