well I played thru the single player demo and got to about level 10 on multiplayer. the single player was good... it was mass effect. it's as streamlined/linear as Mass Effect 2 which I guess was to be expected, but still a bit disappointing as I've been dying for them to open this game up more and make it more free-roamish. But, of course the music/writing/atmosphere/combat are all great. the combat and menus are all almost identical to Mass Effect 2, which is fine, but I wish they would've changed it up a bit more.
my favorite part about the demo was the multiplayer, the only mode there is was like a horde mode, but it's extremely fun and rewarding as you level up just like in single player, and can unlock powers/guns/scopes and upgrades/etc. and this makes it have that addicting factor, i enjoyed it up until about level 10 before deciding to give it a break and now am wanting to go play some more.
I just hope that since it's just a demo, there'll be more in the final game (almost definitely there will be i'm sure). since the multiplayer demo only had 2 different maps and only the one horde mode to play. hopefully the retail release has more maps and different modes, and maybe more specific stuff to spend cash on besides the 2 boxes of random goodies (one box for 5000 credits gives you some random stuff with small chance of getting a rare gun and then the other box for 20,000 credits gives you more random stuff than the other, with a guaranteed chance of getting a rare gun).
all in all I enjoyed both single player and multiplayer demos and will definitely be getting the full game when it's out, but i still am wishing the single player was more open/less "go here, shoot that, go there". i found nothing around corners except one scope upgrade for a pistol, i want more loot damnit.