Depends on which edition you are talking.
RM2? The armor rules have some problems, in that the penalties are probably a little too harsh and armors have a baked-in quickness bonus/penalty, which makes AT 1 better in many instances than heavier armors. I wouldn't say they are entirely broken though: so long as you remember that strength bonuses can cancel out the quickness penalty to the higher ATs, and so long as you have a good number of hit points, you can still find yourself better protected in AT 20 than in AT 1.
RMSS? I don't know enough, but from what I've heard, it might be even worse than RM2.
RMU? I think the armor rules are the best for any edition of Rolemaster. The problems of earlier editions have been largely solved, the baked-in quickness bonus/penalty has been removed, and the higher armors are very effective at protecting characters. The piecemeal armor rules have some idiosyncrasies and unexpected results, but these can be solved by rolling critical/location first, or simply not using piecemeal armor. Some people think the penalties are still a little too high, but I think when you play RMU for a while and appreciate how protective the heavier armors now are, people will come to appreciate how valuable armor now is. I think RMU has done a great job of fixing armor.