Maze design is things like hallways doing switchbacks for no reason, figure 8 loops of corridor that have nothing in them except for one door at each end, that kind of thing. In general, anything that looks ridiculously more complicated than what people would actually ever build.
And in any case, System Shock had five times more of it than SS2. The whole maintenance level was basically four mazes around a hub area. As far as level complexity goes, SS >>> SS2 > Bioshock, the last mostly due to Bioshock being smaller overall. They all kind of suffer from having way more dead bodies and monsters than can be accounted for by the size of their environments, though.
I never got the feeling in Bioshock that I could only go in one direction. You were generally free to dick around all you wanted in areas that you'd already been in, to the point of taking the elevator to completely empty levels. There wasn't a lot of free exploration, but then, I didn't feel like there was in SS2, either. In either game you might have a choice of 2 or three rooms or small areas you haven't been in yet, there's not a whole lot of wandering off into sectors you don't have any business being in.