Gaben is an incredible speaker. Just listening to him talk and from the things he says you can tell he's smart as hell. He has that ability to see things, connections and so on that truly intelligent people have (meaning, not just those who score high on an IQ test.)
Gabe is very different to Carmack, as
milk said, Carmack distills almost everything to a hardware or software engineering view. The lack of business, economics and industry politics skews is one of the reason why I like listening to Carmack.
But Gabe is very business/profit orientated. Remember when he infamously
said:
Gabe Newell said:
"Investing in the Cell, investing in the SPE gives you no long-term benefits. There's nothing there that you're going to apply to anything else. You're not going to gain anything except a hatred of the architecture they've created"
Actually Gabe, as much as a fucker Cell was to work with, in no small part due to the terrible state of Sony's early devtools, Cell was setting the direction of the future of games development. You may dislike (or hate) the architecture but the philosophy of re-thinking game engines down to smaller parallisable tasks to run on lower-clocked or stream processing cores, was obviously the [then] future. To be fair, Carmack also didn't like this development either and was long a proponent for higher-clocked, fewer-core processor architectures.
Gabe's also been outspoken on
Windows 8 app space. Now I was with him on this at first. As a Mac OSX user since 2003, I thought this was a terrible idea until Apple introduced the OSX App Store (similar model to the iOS model) and realised,
as a consumer, it was in my interest to buy software from the app store. There was none of this single-machine licence, the OS would keep it updated, the app was sandboxed to limit rogue app's destructive abilities. Now I'll rarley buy an OSX app unless it's in the app store. There are good reasons not to be in that space, like Parallels and VMWare's products where they can't operative within the sandboxed requirement space, but mostly I simply won't buy applications, utilities or games outside the app store.
Carmack is polarised from an engineering perspective, Gabe is not. That's not to say either is wrong or bad, but from where I sit 99% of the time, which is from a consumer perspective, Carmack's perspective is more relevant. And even then, he's not always right about where technology is heading.