Rammus is overrated. The vast majority of people who play him are garbage at ganking anyways, even with his short cd "fuck your wards" initiation. Even more of them are terrible at keeping up in the game if they fall behind. Which they always do, because they can't gank worth beans.
That being said, if you can do it, then he's annoying as shit because warding has to be changed drastically to deal with him, and that change is more risky because you have to ward deeper to compensate for powerball.