I have a Rottie who is still going strong after 10 years(rigid diet and exercise).
Besides all the good advise already offered(particularly socialization), I would state that Rottie's also require an above average amount of their owner's/family's time just hanging out.
They are incredibly affectionate and loyal dogs and love nothing more than to be with their owners.
They are fantastic with kids, but I think it is pretty important for the kids to be born/adopted BEFORE the Rottie.
I would consider the breed(or at least MY Rottie) to be not particularly bright.....my dog would never earn a doggie university degree(If you want a smart dog get a GS, JRT, or Corgie)....but he's incredibly intuitive.
While ours is still in great health......the biggest fear in my life now is seeing my dog go down hill fast
We will definitely get another....and probably a female as well......our male is pretty big at 50kg with no fat on him.
Seeing all these giant Afghan dogs about(my first trip over here)....I wonder what the story is with them and whether jillions of people coming in and out of here the past decade will see that breed make it's way into the west?