Another one of the many things I didn't like about 4th edition was the short duration spells. I want a return to spells with durations like round/level, minute/level, hour/level, concentration/+2 rounds etc.... I hated that most all spells had the "end of your next turn", "beginning of your next turn" etc durations. I don't mind some spells having short durations but I want a return of the longer duration ones.
"minute/level" or "hour/level" was part of the quadratic wizard problem. When a Wizard goes from level 6 to 7, not only he gets more spell slots, but also the spells he has are more powerful. Hence, while the non spell casters advance linearly (they learn new abilities), casters advance quadratically (they learn new abilities, and every ability they have becames more powerful).
It's a better solution to have "until end of encounter" or "1 day" durations, and balance the spells acordingly to that.