My answer is based on the assumption that I have a reasonably informed view of the designers' goals, and am looking at it strictly of what they could have done to better meet them. (I happen to like where they were headed, but it isn't the only 4E design I could have liked. Give me another set of designers and goals, and I'll comment on that.

)
They didn't go far enough in two areas:
1. Didn't push the concept of rituals as broad and deep as it could have been pushed. Me, I make up my own flavor, but people that feel the lack of flavor could have been a lot more happy with more effort in rituals, especially expanding it into
options for craft skills and other sim elements that not everyone cares about.
2. Instead of a long list of powers for every class, should have pushed the power design even more, into something akin to a power-building concept, with rules. In effect, do a Hero or GURPS lite version of powers, with examples. This would have been a very clever compromise between people who enjoy the class/level part of D&D but want more flexibility--keep the classes, levels, and stuff attached to them--but make a separate system for the powers. The funny thing is, with the powers as written, they aren't that far from that now. They just weren't as explicit about it as they were with the rest of the system.