I've given the multiplayer mode a try now. At first it looks very well-crafted: You pick a character - those range from an engineer to an athlete to a fat cat, and that's where the differences end - and proceed to the prologue, where you wake up on the floor recovering from your first plasmid splice. Then you can roam around the apartment. From there you can select your weapons, plasmids and tonics, put on party masks, listen to characters' audio logs, and uh, play a little music. It looks nice but there's nothing in there a menu couldn't do better.
The match selection is a bit confusing. It doesn't have dedicated servers, so no user-friendliness there. It gives you a "Find Match" option to select one of the standard mutliplayer fragfest game types with a slightly different name. Then, it appears that it randomly groups people with the same game type selected into a match, but I'm not sure of that. There's no other option available than to select a game type. After that you wait until enough people join in and the game starts.
I enjoyed the gameplay itself very much, however. It keep things much simpler than conventional Bioshock: Two weapons, two plasmids, and three tonics. You can arrange different combinations in three available item sets, and swap between them while waiting to respawn. You start with a pistol and shotgun, electro bolt, incinerate and winter blast. As you gain levels, or ranks, different weapons and plasmids become available, but there doesn't appear to be a choice in which you do and don't want to get. You can get points by killing enemies (duh), photographing their corpse for a damage bonus (a creative alternative to teabagging), hacking turrets and machines (vending machines are refill stations for eve and ammo, you can rig these to explode), finding Big Daddy suits (these spawn in the map from time to time, haven't yet found one), killing players in Big Daddy suits, and picking up vials of adam that are scattered across the map. So, plenty of opportunity to get up in ranks if you're not good at shooting. Gonna try the other game types soon, too.