I was going to post pretty much this.Previously posted in another thread, but worth repeating:
1. Powers For Everybody
Every character should have options beyond "I make a basic attack." You should not have to play a spellcaster to unleash a more powerful attack or trigger some beneficial effect when you need it.
2. The Encounter Power
There should be encounter powers to straddle the middle ground between vanilla at-will abilities and more significant daily powers.
3. Healing Surges
Healing surges ensure that healing powers generally keep pace with character hit points as they go up in level. As a reserve of endurance that usually goes beyond what the PCs can bring to bear in any single encounter, they also enable multiple encounters per day while retaining the possibility that PCs could be dropped in any encounter. Possibly, they could be reflavored and renamed as hit point restoring powers instead of healing surges, e.g. instead of having 12 healing surges, a paladin could have 12 daily uses of cure light wounds.
4. Skill Challenges
Skill challenges provide a structure to supplement the normal free-form approach for resolving non-combat challenges that are more complex and require more than a single skill check. Perhaps they could explicitly be made more flexible - for example, the DM could award multiple successes and even automatic successes for good ideas.
While the biggest problem of 4E was the overly constrained design of the power system, the idea that every class should have powers is definitely its strongest idea.