Henry
Autoexreginated
In my PERSONAL OPINION, I would argue that while 4e is a lot of fun, there's not a lot of creativity. It's all a lot of very straight-forward X, Y, Z. 3rd seemed to take creativity overboard, with so much customization it became difficult to keep track of it all. When I transitioned between 3e and 4e, this was probably the most profound feeling I got out of it. I felt it was easier to have "fun" in 4e, but my creativity felt stifled.
My experience with both differ -- the charts on Pages 42, 184, and 185 of the 4th edition DMG show someone how to be immensely creative, while giving a framework that will help a DM not accidentally over- or under-power what he sends at his players, or whatever non-"powered" creative solution his players want to try against the challenges they face. If he wants to overwhelm the players, he'll full well have the math in front of him to show him that's what he's doing, intentionally or not. How the DM creatively expresses the challenges his players face is completely up to him, with only guidance to power level of the threat.
My current and previous experience with 3.x is that so many corner cases, variants and options are presented, that the opposite, namely "analysis paralysis" can result in both DMs or players. Do I threaten the players with a 4th level sorcerer and his warrior-1 cronies, or would a cleric-3 and his zombie horde be more effective? Do I want the enemy to just bog them down, or will a party without a cleric be totally screwed? Would a party with a cleric find it a total cakewalk? Would the sorcerer-4 obliterate the party with spamming scorching rays, or should I just equip him with burning hands and web spells and under-play his tactics? Or would my specific group of players totally destroy him without losing a single spell or hit point? And it takes a LOT, a LOT of time behind the DM screen to answer these questions properly.
Even in the case of a refined version like Pathfinder, which I enjoy the heck out of, the designers at Paizo have difficulty answering this question. To vary a challenge, they'll give the villain a shortspear instead of a longsword or greataxe, so he won't be as damaging, and he'll have toughness and improve initiative instead of power attack and cleave, when in his right mind he should be fighting with the more effective weapon, or the superior villain will gloat for three rounds until he gets knocked down to half his hit points, so that the party stands a chance. In a way, too much detail can limit plausibility of actions, to explain why the DM is lightening a challenge to make it more appropriate instead of a vast challenge or suicide.
In short, I don't think the question is "how creative should 5e let you be?" it's "how creative should the players let 5E be?" Because that's why it's being made in the first place, when you get down to it. Too creative with the rules interpretations differently from what came before, and people won't buy it.