I miss having wizards and other spellcasters that are able to do more than just blow things up in combat. D&D, for me, included wizards being magical swiss-army-knives, with multiple cool spells usable for many different purposes. Now, spellcasters are able to blow things up in combat and very little else. Rituals are a pale shadow of the D&D magic system, because they take too long to cast to be useful in most situations, and cost way too much gold to use very often.
Don't get me wrong. I like 4e, but I miss being able to use magic for creative problem solving.
I also miss magic items with multiple abilities, like pre-4e staves, and many pre-4e wondrous items and weapons.