First than first sorry for my not perfect english guys. I hope that you will read and understand my opinion about the demo anyway..
Since I downloaded the demo I've played it like every day..I am lv 104 and I found this multiplayer
very interesting in all ways..
What I like:
No lag problems
Maps are very interesting and immersive..(reminds me the old missions of ME and ME2.. :') ).
Game chat is ok, no difficultys to speak with team mates.
All races and classes are pretty balanced, so the player is not compelled to choose the race-class that is best than others but the one that he likes straight from singleplayer experience..
The time that the team takes to complete a mission is about 20-25 minutes on bronze and silver difficulty. A perfect time for a play, and people will not get boring..
What I dislike:
The random package system. I've played for hours and took a lot of credits for veteran package but I didn't find nothing really considerable like races or customizzation..just updates for weapons that I don't use and things like that..
I think that the best way is to fix that..leaving the random packages as well, but give the possibility to "buy" a race, a weapon and customizzation for more credits..(example: Race - 100.000 credits, Weapon - 75.000 credits, Character Customizzation - 50.000 credits)
Enrich the multyplayer with more races and customizzation, give the way to choose a geth, or batarian, (vorcha and maybe a volus, I know that is a slow race but maybe can run fast like other races using a jetpack or something like that?why not..

) in the future by some dlc or update..
Same thing for customizzation..for example, when I use a human is ok because he has the armor that covers all his body and face so I can select a color for it, but when I use a drell, and my team mate uses drell as well there is not difference between them..same thing for krogans,asari, turians and salarians..they are looking the same like gemini, maybe if you give the way to choose the skin type and color with armor color as well since the race is unlocked it will be a small but very significant thing, I'm not the only one that likes a fully 100% customizzation..

Like for armor, I'll like the way to customize my weapons color..is not so important to say but anyway it will be great to have this possibility..
I didn't found so important to choose a male o female human because they have the same stats and abilitys..But I don't know why you didn't gave the way to choose a quarian male but only female for example..
I think that customizzation will be better if a player choose a simple human and then using customizzation he can choose a male or a female..same thing for all races where it's possible..
The heal button is A,the same for run,jump, cover and activate..in my opinion is not the best button for healing because it happened for a lot of times that my character ran or jumped when i was trying to heal a team mate..maybe should be fixed for a other button..like X..
Cover sistem is not so perfect, sometimes my character jumps when I try to let him cover..
I think that there is nothing else that should be fixed in the multyplayer..I really like Mass Effect since it cames with first episode, honestly I did'nt believe in multyplayer becuse I thought it wasn't that type of game that needs it, but I changed my idea since I've try it out, beautyful..
Great work for all Bioware Team.