What groundbreaking logic it had implemented?
We consider a lot of what it introduced as "just videogames" nowadays, so it can be hard to spot. Comparing can help - consider Doom (1993) versus Wolfenstein 3D from the previous year:
* walls at angles besides 90 degrees
* floor and ceiling textures
* multiple kinds of ammunition
* lighting
Why it is ported to various platforms
It was open-sourced in 1999, so it's partly about availability. I suspect it's also because it's _possible_ to port to lots of things; it benefits from specialized hardware for graphics acceleration but doesn't require it.
