Personally I feel PiD was a much better game than Wolfenstein, partly because of the adventure/RPG elements, partly because of the horror atmosphere. The UI was less immersive however. But the game certainly had very interesting elements. For example there was a level that was randomly generated every time. Some monsters could only be killed when frozen (using a special "blue crystal") otherwise they'd be invisible and be impossible to kill. It was possible to talk with dead human corpses using a "yellow crystal", etc… There was a special room that would drain the oxygen and only by speeding up the time somehow (perhaps using another crystal?) one could survive the room.
And some things Marathon certainly did better than Doom. For example it was possible to look up and down, the lightning effects were more impressive, there were some physics, etc ...
Of course the guy that wrote the Build engine (of Duke Nukem 3D fame) was probably at a more-or-less equal skill level as well.
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[0]: https://en.wikipedia.org/wiki/Jason_Jones_(programmer)
There's probably legendary but unknown programmers at place like EA or Sony.
There are plenty of legendary gamedev engineers who are somewhat known, most of them hang out on Twitter (Carmack has a great Twitter account IMO)
I've only worked in the industry for a little over a year now, but I've heard some great stories from the senior engineers.
Yes. In fact, he is probably a 100x programmer.
Carmack didn't exactly create Commander Keen all by himself. John Romero did some programming, and the level editors and other tools like the installer. Adrian Carmack did the art, Tom Hall came up withe gameplay ideas and level designs. Besides, Keen wasn't anything amazing in terms of a game, other than the fact that it was one fo the first popular side-scrollers on the PC.
In the end, Keen was a basic side-scroller. Of which plenty existed over the years. Shareware, hobbyist, and professional game developers were not in short supply.
Wolfenstein 3D and Doom. Again, Carmack wasn't the only programmer. Again, Romero wrote the level tools. Dave Taylor also had programming duties. Heck, id even farmed out the sound code! Wouldn't a true 10x developer bang out a sound library in his sleep?
Quake rolls around. This time Carmack has brought in re-inforcements. Mike Abrash for his vast knowledge of graphics coding and optimization, and John Cash for the networking side. Dave Taylor wrote the sound engine and some other things. Zoid ended up taking QuakeWorld.
Around the Quake 2/3 time, Carmack started to come into his own. They brought Brian Hook in help do 3D graphics, but Carmack created a level editor as his 'first win32 program', even though he eventually passed it on to Robert Duffy. Carmack was really doing a lot of things with 3D graphics and hardware at the time.
Let's not forget his side projects like graphics drivers and porting id games to things like the iPhone and SNES.
I'll end this by saying at the very least he had a huge hand in getting PC gaming going in the right direction. I also love his willingness to release the source code to their products. But was he a '10x programmer'? Maybe he was just really good.