From what I've gathered there's 50SP stages with bosses. So about as robust as a SP bomberman can get
8 stages were shown for Multiplayer (online and off) but they mentioned that you can unlock stages and characters.
There was also slots for 4 more in the vanilla MP modes and another panel for a potential 12 more stages.
Whether they're alternatives of the original or completely new we don't know. Point is up to 24 stages MP.
Plus a ton of unlockable vanity items and stuff like that.
As for gameplay, it's bomberman you either like it or you don't. 8 player online will be nuts though