Since I've used this game system but I still own all of the stuff against the day I might want to play it again.
The basic concept of the game is simple, each character has 10 stats such as strength, intuition, etc. that are rated 1-100 and a bunch of skills rated from -25 to 150+.
There is lots of classes, most of which are magic-users of some variety. There's lots of overlap between the classes so there are at least 3 different ways to make any character archtype you'd like. Fun for replayability.
The combat system sounds simple and has some neat critical hits and fumbles but here's where things start breaking down. The players have to be willing to do a LOT of math and consult a lot of charts to find out what is happening. Characters can suffer from continuing blood loss, after-effects of criticals, and such things as being stunned by seeing their leg chopped off. Very realistic and morbidly humorous. Also VERY slow. Battles that take a minute of game time can easily take 2-3 hours of real time. I don't know about you, but I've got better things to do with my time.
The other problem with the game system also naturally flows out of the combat system. If combat is so bloody, how do the characters keep going? Lots of spells. Lots and lots of spells. You can't use this system for low-magic situations because the characters would be incapacitated by a bar-fight for weeks. Realistic but not fun.
Managing all of the wounds, bleeding, rounds of stun, spells, spell points, effects of spells, and spell point-enhancing items can be quite a chore as well. This isn't a game system for the faint of heart, folks.
So you're probably wondering why I'm giving this game as high a rating as I do. The reason is also simple, I love Middle Earth and I've yet to find a game system that does more justice to Middle Earth than Rolemaster.
Yes, the system is dated (dates back to the late 1970's, in fact). Yes, it's clunky and requires a calculator and 3 sheets of scrap paper per player per game session. When you bring it all together in Middle Earth it still plays great!