I didn't get past room 11 at the PAX East demo (I only gave two quick attempts before giving up the controller, wish I had stayed longer to be honest but I didn't want to hold up the line
), but I think it was just the Endless Drop mode; so I didn't run into the stone golem. Still, based on the descriptions of bosses I'm actually hoping we see a lot of bosses even larger than him. When I heard room-filling, I was thinking bosses that literally encompassed the room, maybe a worm boss that would dive in and out of the arena and dig behind the walls of the area, or a giant wall face with hands, crazy intimidating stuff like that. It would also be cool to have elevator sections like in beat em ups where you have to survive enemies falling down onto the descending platform for a certain amount of time until reaching your destination; that would be especially interesting for a boss fight. Maybe the platform could actually BE the boss?
I'd also like to see smaller mini-bosses, perhaps a crazed delver lost in the labyrinths of The Drop would attack you (Butcher anybody?