This is everything that I liked about 4e despite not being a fan of the game as a whole:
1. Removal of Level Drain
2. Removal of 3e XP Costs
3. Balance between the classes at all levels
4. Races
a. Removing the non-biological aspects of race (should have gone farther) and making them feats.
b. Elf/Eladrin Split
5. Classes
a. Ranger as non-spellcaster
b. Warlord (with caveat)
6. Hit Points (with caveat)
a. more to start with
b. No hp bonus per level from con
7. Character Builds as examples for for tailoring the class
8. Heroic Tier Multi-classing
9. Saving Throws (with caveat)
a. Single progression
10. Combat
a. Martial characters get cool things to do (w/caveat)
b. Death and Dying
c. Non divine healing (w/caveat)
11. Disease Track
12. Magic Missile requiring a to hit roll
13. Skill Challenges (w/caveat)
14. Rituals (w/caveat)
15. Feywild
16. Backgrounds/Themes
17. PHB2: Bard (with caveat), Barbarian (with caveat), Druid, Shaman (w/ caveat), Gnome, Half-Orc
18. Minions