I've played Role master briefly in highschool. The system left such an impression on me that I try to incorporate it's best features into my home brews.
My major love/hate relationship with it is the level of detail on the crit charts. It shows an amazing amount of depth and effort into combat, however, at the same time it also shows a lack of imagination on the DM's part. They are limited to following charts which leaves a bad taste in my mouth.
When I DM with my SimpleSystem, I have 2 values that matter when attacking. Ability to dodge and armor rolls. Based on how high a roll is over dodging and armor value affects how I allow the attack to happen. In one case a player with significant skill and a large sword rolled extremely high against goblins. So those goblins lost limbs and started fleeing the battle. In another case a ranger proficient in bows nailed a surprised enemy in the neck preventing him from calling friends.
It helps mediate between 2 issues. First being the difference between hit points and health. In other words, how many hitpoints is a severed arm worth? They are differing concepts that Rolemaster helps to bridge being that it's rare to kill a monster based on hitpoints rather than disable them due to critical hits.
The second issue is aimed shots. What stops an archer from saying "I aim for the head" every single time? It's easier to say "well obviously you are always aiming for the head, now here's what happened based on your roll". There's a way to prevent players from attempting to break a system by presenting them with optional events rather than enforcing more rules.
I also love how rolemaster blurrs the lines between weapons. D&D, and many other systems, follow this pattern where the weapon that you use, and what it's made out of, has more to do with damage than your skill with that particular weapon. Can't remember what system it is, but there is one edition where the katana is the most powerful weapon and there's no reason to ever use anything else. It encourages min-maxing and power playing where a dwarf warrior will use katana's and pole-arms in place of war hammers and axes. From my experience in rolemaster you just choose a weapon type that your character would use and may improve profieciency in said weapon, and can rely on all of it's advantages and weaknesses.
Now that I've talked the system up so much, I just may be up for a game!