Some of the things I liked about 4E have been mentioned above -
(1) monster/encounter design was a breeze compared to 3.5E (especially for somebody anal like me that has to fill out every skill, feat, spell slot, etc for high level baddies)
(2) Racial powers
(3) every party doesn't need a cleric.
(4) Standard/Move/Minor each round
However, the big thing I liked about 4E is that it got rid of the 15 minute adventuring day, at least in my game. In every previous edition, once the cleric was down healing and the wizard was down in spells, the party would stop for the day to rest & recover. In 4E, you can keep going because a lot of those encounter powers are pretty good, and you keep going until you're out of healing surges. Most games I'd been involved with in the past from the late 70s and on were centered on (usually) one big encounter per day, then the party rests & recovers afterwards.
(1) monster/encounter design was a breeze compared to 3.5E (especially for somebody anal like me that has to fill out every skill, feat, spell slot, etc for high level baddies)
(2) Racial powers
(3) every party doesn't need a cleric.
(4) Standard/Move/Minor each round
However, the big thing I liked about 4E is that it got rid of the 15 minute adventuring day, at least in my game. In every previous edition, once the cleric was down healing and the wizard was down in spells, the party would stop for the day to rest & recover. In 4E, you can keep going because a lot of those encounter powers are pretty good, and you keep going until you're out of healing surges. Most games I'd been involved with in the past from the late 70s and on were centered on (usually) one big encounter per day, then the party rests & recovers afterwards.