Right now, we're taking a break from our 3E campaigns to play a Mage game set in 1920s New York.
It's lots of fun, but good gravy, the lack of rules does NOT make the game easier to adjudicate.
Setting aside the abysmal organization of the rules (as one small example, Willpower is a vital stat in the game, almost as important as HP in D&D, but the rules for it are scattered throughout the book, and the index's only reference to Willpower points to a small clause explaining how it's used in casting spells), the rules are very open-ended. The GM determines everything from how valuable a particular stat might be (the "node" stat gives you from 1 point of magical energy per week to 10 points of energy per week, with no guidance on what the GM should choose) to what level of success is required to pull off a particular effect ("You want to weaken that wall? Okay, I'm going to make that, say, five successes. No, six. No, five.")
The big tradeoff we see is that magic is extremely open-ended in such a system. If you as a player can think of an effect, there's a mage out there who can pull it off. Coming up with nifty things to try is great fun: you don't have to look at a spell list to determine what you can try to do, but instead you can think, "Okay, he's getting ready to blow the Trumpet of Zombie Raising? I spit out my bubblegum and throw it at him, and the trumpet fills with bubblegum, making it unplayable!" and generally you've got a shot at having it work.
Of course, the GM figures out how many successes it'll take, and if the effect goes wrong, the penalties for failure are limited only by the GM's imagination.
D&D is different. You want to try an effect? Chances are good that somewhere in the rules there are guidelines for the action. The game's arbiter doesn't seem arbitrary, if they know the rules well: the game is exquisitely balanced, and the rules are very well organized and consistent.
But at the same time, characters are far more limited: because the rules are so comprehensive, it's very easy as a DM to assume that actions not covered by the rules are either impossible ("No, of course you can't leap onto the giant, climb up to his face, and stab him in the eye -- show me the rules for climbing hostile creatures!") or have no rule effect ("You leap from the balcony, holding on to the chandelier's rope, and swing down at the villain, trying to kick her in the nose? Um, okay -- make an unarmed attack roll.")
I think the challenges for a Mage GM center around making the game fair (so that all players feel like they have an equal chance to do fun stuff), and the challenges for a D&D GM center around making room in the game for creativity (so that players don't feel constrained by the rules).
I think, getting back to the OP, that 1E D&D was much closer to Mage in feel: there were several unrelated systems throughout the game, and the rules weren't organized very well, and there were plenty of situations that the rules didn't cover. Old-school DMs didn't need nearly as much rules-knowledge, had much more flexibility when dealing with bizarre occurrences -- but at the same time, it was a lot easier under old-school D&D to favor one character or class over another, much easier for some characters to get left out of the action.
Daniel