..kinda sucked. Let's not even get started on Cyborg Commando. I sorta liked Mythus/Dangerous Journeys, but it really didn't offer anything that Runequest couldn't do better. The implicit question here is did Gary Gygax get lucky writing D&D and just sucked as a game designer otherwise? Nothing else he did ever approached D&D's level of success. I remember his posts on Dragonsfoot; he'd usually want to talk about Lejendary Adventures, but was hounded with rules questions concerning AD&D. Literally 30+ years after the game was published. Was he simply a one-trick pony, analogous to multitudes of rock bands with one good song?
I'd say no, because of one fact: no other rpg ever written has been able to overtake D&D, either. RQ and The Fantasy Trip and Tunnels and Trolls, Vampire, Chivalry & Sorcery, GURPS, Traveller, HERO, and probably a metric ton of others...these games are all popular within the confines of the rpg community. We'd call them successful, most likely, but in the grand scheme of things, they're irrelevant. No one has ever heard of Runequest except other gamers. D&D, that's in the lexicon of modern English. I don't think it's possible to ever make a game more widely known and representative of rpgs than D&D as, for all intents and purposes, it is essentially everything that constitutes roleplaying. It was the first and defined a whole genre of new games. You cannot supplant D&D, and anything that follows looks like a clone of sorts, even those that differ in wildly imaginative ways.
At one point I decided I was only going to play GURPS, and only buy GURPS supplements. I figured whatever D&D did, I could do better with a unified gaming mechanic and much more realistic rules. Any other game that was published, I was sure GURPS could emulate the setting. This lasted about one month as I purchased Mekton Zeta. GURPS couldn't do giant robots beating the shit out of each other very well, but MZ could. I tried to run a fantasy campaign using GURPS not long after, and all the house rules I came up with ended being nothing more than ways to copy D&D-isms. Dungeon Fantasy does basically the same thing. It's pretty good, but honestly, why bother? You can play an easier game, like Labyrinth Lord, and be done with it.
It's sometimes the case that an artist comes right out of the gate with his magnum opus, and forever seeks to duplicate his efforts, perhaps in an effort to duplicate success. I don't think Gygax ever did so. It's my feeling that he knew D&D was the best he could do, or really, anyone could do, and left it alone to make other games. Artists create art, game designers design games, even when their best work is in the past. Sometimes you can build an empire on one insanely popular work, as did Gygax. Jimmy Buffett owns an island and has a chain of restaurants based on a stupid song about margaritas, and like Gygax maybe he realizes it's not a bad thing to ride that pony into the sunset.