- Fighter and Healer - An combat system with hit points has two obvious "roles": The guy who deals damage to the enemy (4E striker) and the guy who heals damage dealt to his allies (4E leader). 4E expands on this by adding a guy who inflicts status effects (controller). You could argue that a defender heals indirectly, because healing powers are more effective on him (they heal a percentage of his max HP, and he gets a higher total than others).
- Skill Monkeys were taken out of 4E - or rather, everyone is a bit of skill monkey since everyone gets a similar amount of skills.
- Holder of Win Buttons is the odd guy out. A Wizard in earlier editions get a limited number of spells that can solve problems when the party's fighting tactics or puzzle-solving skills fail. Sleep wins combats at low level, Fireball wins them at higher ones, Knock sorts out pesky locked doors if the thief is out of commission, and then there are all the divination rituals for when the party is really stumped. Of course, at high level, the Wizard get too many win buttons and goes from "useful party member" to "party leader with three pets".
Anyway, there are two oddities with the old roles, at least as they appear in D&D 3.
- Nonstandard classes don't fill the roles well (and don't come with instructions).
- The Druid is a worse healer than the Cleric - the same healing spells are higher level for him, and he gets no spontaneous casting of cure spells - but gets some win buttons to compensate.
- The Bard (and Monk) can't fill in for a Rogue - at least not in the trap disarming department.
- The Ranger, Paladin and Barbarian do well enough at replacing the Fighter.
- The Sorcerer can blast better than the Wizard, but is out of luck when he needs an obscure utility spell.
- The Druid is a worse healer than the Cleric - the same healing spells are higher level for him, and he gets no spontaneous casting of cure spells - but gets some win buttons to compensate.
- Splitting of spotlight. First the rogue disarms a trap and unlocks a door. Then the fighter rushes in to kill everything, while the cleric stands by to heal him. Then more traps - the thief gets the spotlight again. Meanwhile, the Wizard is standing by waiting for the best moment to step in and press one of his "win buttons". This is a design that's worked for 30 years, but not one I agree with, and plenty of other game systems have changed it.
Of course, D&D 4E missed an opportunity too. Everyone has a combat role, and is relatively competent in skill challenges. However, there is little differentiation in what skills characters have. There is some, in that Arcane characters are likely to have Arcana, Divine ones probably have Religion, Primal ones have Nature and Martial ones get... heck if I know. Still, the roles make it easy to get a good spread of combat roles when characters are rolled up, while skills still have to be doled out manually.
I don't have a better solution. The problem with delineated skill-roles is that the obvious division - Talker, Mechanic, Athlete and Living Encyclopedia - split the spotlight again. The Talker rules social encounters while the Athlete and Mechanic disarm traps. The best is probably to focus on the skills that your stats work with - a diverse group should cover most of the stats, and that provides a natural division of skills. Watch out if everyone plays Arcane classes, though - you'll rock at intelligence-based skills and be mediocre at the others.