I think it's a good size. Keep in mind that rabbits need lots of play time, and no cage will ever fill a rabbit's needs the way it can for a pig. Also, the multiple levels are great for rabbits. Mine get a lot of use (and exercise) out of them.
Although I would change the layout of the upper levels- do they really need the steps? Could you move the floors down a square and remove the steps? It would make it more open and easier to play in. Just my opinion.
they're house rabbits.. and litter box trained, so they're out when I'm home. the cage is just when I'm not home or asleep. When I am, the door to the cage is open at all times (and they usually wind up spending most of the time inside the cage anyway, or coming out for 5 minutes at a time then going back in again)