BTW, these were my concernes: (I'm glad that I'm not the only one who noticed many of these issues... I still hope most of it is a demo exclusive thingy)
1. It's full of bugs
a) disappearing and backshifting reaper : I'm talking about the first one you come across in the game. While you're talking to the kid it moves by the building you are in - at least its legs do (you can clearly see it), but when you get out of the building it's back in its original position again, and last but not the least it simply disappears after the fall you make when the warship goes down). Mysterious to say the least.

disappearing gun during animation : It happens in Surkesh during one of the cutscenes at a checkpoint.
c) invisible turret : it happened to me once. One of the turrets seemed invisible, but it was fiering at me as hell, though the little red frame appeared when I aimed at it with "my" gun, so I put the sneaky bastard to rest.
d) Wreave's voice is on the radio instead of Wrex's.
2. It has unresolved motion and controll issues:
a) Sprinting feels unnatural and it looks like you just float in the air. Let alone there's no exhaustion as such.

The problematic cover system: There were occasions when I simply couldn't get into cover, but kept rolling against the wall. There was one time when I tried to shoot from behind cover and Shep didn't lean out from behind the wall but leaned against it so I could only shoot the metal plating on it. ME2-s cover system was a lot more dynamic.
c) The omni-button: I'm talking about the spacebar here. Sometimes tends to get irritating then you want to do one thing with it but you keep doing something else.
d) Basic movement speed is way slower then in earlier installments.
e) Lack of the holster gun option.
f) Sensitivity of power buttons are pretty bad: I happen to be a pc player, so I don't know wether it happens to console players, but it happens quite often that whenever I clikck on a power button with my mouse, nothing happens, so I have to repeat it a few times in a row. It takes a lot from the combat dynamics.
3. Graphics and animation: I find the graphics a bit ambivalent. It is very nice and spectacular and seems to be very unpolished at the same time. IMHO ME2 looked way better when it comes to actual graphics, lighting and colours. Animation is a lot better though - and it is a huge improvement from all the previous games, except for facial animation and few minor issues. I loved the small details and the delivery of animations between parts where you controll Shepard and cutscenes. It flows really well.
a) Textures are blurry and their resolution is pretty low: It's especially evident when you look at the characters clothing or at the buildings in the backround (they seem to be unfinished models that lack detail and depth).

I miss the movie grain effect very much.
c) Some tiny issues with background animation: 2D husks running sideway, fighters shooting at reaper fly through the reapers etc.
d) Facial animations and lipsync are lacking and unnatural sometimes (especially wiht Anderson) compared to the previous games.
e) Water animation is pretty bad in the prologue.
f) Backgrounds, sets seem to be a bit lifeless sometimes (especially in Surkesh).
g) It's very annoying when the bodies of shot enemies disappear just like that without any animation and it happens right in front of your eyes after about 2-3 seconds.
3. Story, script, dialogue system:
a) Autodialogue and lack of choices. In the demo the good old dialogue and choces and concequences system which both played a huge part in making the whole series remarkable and so popular are pretty much absent. Hopefully it's a demo only issue.

If this is the real prologue of the game indeed, then I got to say that it's the one that is the worst by far in the series - no matter the potential and the spectacular setting. As a script-piece and especially as prologue it does not work, it leaves nothing but confusion and questions in the players' minds (even in those who played the firt two installments). It does not let you get involved in the plot at all. It rashes things and lets no time for warming up for the events that await you. Even as an in medias res it doesn't work too well. A slower pace, more sensible dialogues and an opportunity to get familiar with past and recent events and to be introduced to certain individuals would have made it a lot, I mean a LOT better. Don't forget that these are the first moments of a very anticipated game. I hope it does not resemble the whole script and the pacing of the whole game. It's pretty sloppy at places and uninspired. I also miss the trial as a consequence to Arrival - it could have been a relevant scene plotwise. I could live with it though.
c) Some of the characters are out of their characters in the demo (e.g.: Wrex fearing to land with the shuttle because of potential danger... I mean... come on!)