There certainly wasn't enough wrong there to start throwing about wild declarations about this game being a disaster, as many in this thread are doing.
The framerate in the beginning was pretty abysmal and some of those HUD elements were annoying, but otherwise I had little issue with the demo. I thought the sound was impressive, the art direction seemed cohesive, and the animation was well done. I'm not going to say that the demo was amazing. However, it is worth considering that it isn't wise to draw such conclusions from a specially produced demo that was made during crunch time for the full game. From past postmortems of Irrational games, I know that they spend large amounts of time creating specially produced demos for show, and considering that they are in the middle of crunch on the retail game, it would not have been wise for them to divert time and resources to polish this demo to perfection when time and resources are at an absolute premium to get the game out the door.
The AI could've been more active, especially with using the zipline stuff. The thing is, when games are demoed, the difficulty is usually turned down for demonstration purposes. It's quite a stretch to declare that the AI overall is poor based on a minute long encounter in what was a relatively small area in a specially-produced controlled demo.
Also, people are way overreacting about the damage done from bullets. Every "Shock" game has had resilient enemies, weak guns, or both. And if guns were as powerful in Infinite as they are in you average shooter, there would be no need to use the Plasmid powers, explosives, or the "tear" powers that Elizabeth has. The plasmids used and the explosives sure looked like they packed a punch.
Not every shooter has to have you cut through enemies like a hot knife through butter.
Let's put this in context: they just showed several hours of the game to journalists and let them play large portions of the game. Previews and impressions of those who have played it from this material were quite positive. And yet, based on a specially-produced couple minute demo produced in the middle of crunch time in a tumultuous dev cycle, people know that the game is garbage, huh?
I'm not convinced that the game will come together perfectly yet (don't have it preordered!), and it certainly could fall apart under the weight of its ambitions, but there simply isn't enough wrong here to justify the GAF overreaction we have here.