I'm still not sold on the new HUD, nor the command interface. They've managed to leave many questions unanswered, such as the existence of MP and how the various weapons are now summoned. As Zonerunner said, concerns about combat and gameplay as a whole have emerged from this showing of the game.
While Noctis does bring out his "Drive Blade", a dagger, greatsword, and a spear, there's no apparent separate interface for this. Magic seems to be devastating and without limits, effectively simplifying the game. Combination attacks seem to be a major mechanic of combat, as they occupy the 2 lower command slots during this demo.
Warping isn't as flashy as it was last year. The modern cityscape, while comparable to Lucis in construction, is entirely different than the gothic, royal citadel from E3 '13 - most notably being much smaller and condensed.
This may have been a mere demo with few actual aspects of the game instanced, but it's relatively concerning.