Actually, he's pretty much right. Sometimes I'm astonished that D&D was ever popular.
I think D&D's early popularity can be broken down into two waves.
First, it's easy to forget just how revolutionary the idea of a roleplaying game really was. This alone was enough to entice the geeks and wargamers. The latter group, in particular, was prepared to untangle the glorious mess of OD&D. (And it's also easy to forget how popular wargames were: They were on the cusp of becoming a mainstream entertainment in the late '60s and early '70s. There was a massive, existing player base for OD&D to tap into.)
Second, I don't think it's a coincidence that D&D's broke into the mainstream
after the first basic set was produced in 1977. Holmes and then, later, Moldvay, Cook, Marsh, and Mentzer were all able to clean the system up and make it ever more presentable and accessible. The most accessible editions of the game were produced from 1977 to 1991.
The importance of the dungeon crawl really can't be underestimated, either. It remains the most robust adventure structure ever designed for an RPG: It's easy for new DMs to both create and run successful dungeons.
(Successful in the sense that it's very, very difficult to create a dungeon in which you run into the "I don't know how to get the PCs to the next bit of the adventure" problem. By contrast, this is very, very easy to do if you're creating a murder mystery.)
An RPG's success relies on its ability to create Game Masters. D&D's dungeon crawl makes it ideal for creating GMs out of people who have never played an RPG before.
3e, while my favoured edition, is horribly complex. And, annoyingly, it really doesn't need to be - there's the kernel of a really elegant and simple ruleset in there. It's just a shame that, even in the core rulebooks, it's buried under a mountain of detail, modifiers, and math. Oh, the math...
You should check out
Legends & Labyrinths. (With
previews happening here.) It's all about finding that elegant and simple ruleset lurking under the mountains of detail.