Well, in OD&D, magic-users in my game start with all 8 first-level spells. Most are very intuitive: hold portal holds a door closed; sleep puts creatures to sleep; charm person doesn't even have a duration, but instead lasts until dispelled. I can tell my players not to worry about the rules too much.
But with 4e, I couldn't do that. The players need to know the rules, or else the game grinds to a halt. From my group of 9 players, only 2 bothered to learn the rules well. In OD&D that works. In 4e - not so much.
Moreover, in OD&D, 1st level magic-users can only memorize 1 spell at a time. They only need to keep track of one power. At first level, 4e character needs to 2 at will powers, 1 encounter power, 1 daily power, possible 1 or 2 class powers, and 1 racial power. That's a big difference.
Once again, I really like 4e. I think the basic system has huge potential. I really would have liked to see a second edition of 4e.