Hi B Hanson,
I'm sorry I didn't notice your reply/request earlier than that.
Your question is a huge one and at the moment I don't know from where to begin.
We have of course written totally accurate and detailed Campaign Diaries but unfortunately those are in Finnish only. Reading those would have explained a lot.
First, we own every single RM book ever published (in paper versions) except 1st edition Boxed Set. We use some rules from every one so our system is quite an hybrid.
I'll start from the challenges. I've had to adjust the challenge level progression so that the normal "Hard -10" and "Extremely Hard -35" are actually percentages. So the character with Fly-spell who tries to do Extremely Hard Maneuver using his Fly skill of +250 would face the challenge of -35% leaving +163 as his skill. Make that Sheer Folly -50 attempt and it would be +125 before roll. Absurd -75 would leave just a +63. This is not used if the skill is <100. The same goes for every disadvantage the character has. If he has for example -20 from some wound, it would be -20% to any Moving Maneuver BUT only the highest percentage counts as a percentage. So if you have multiple minuses only the highest would be percentage and others normal minuses.
At some point we were seriously tired of normal skill checks to be either extremely successful (any roll except low open-ended would succeed) or total disaster (rolls 1-5 usually). There seemed to be no middle ground or normal failures ever unless something very strange was attempted. That was contrary to real life when we sometimes fail in routine skill checks but not fumble dangerously. So we invented "UM Failure". UM Failure is the failure range above the Fumble Range that increases when the difficulty of the maneuver increases. With Medium it's 6-10 and with Sheer Folly it's 6-40. Hitting that range with UM D100 means something unpredictable but not so dangerous happens and the total skill bonus suffers -D100% disadvantage AND the percentage from the difficulty rating. So the player rolls D100 and cuts that away from his total bonus, then applies the original roll. This makes the players really consider harder than Very Hard (UM Failure range 6-20) attempts. For example player with +300 total skill bonus tries Extremely Hard (-35%) task with UM Failure of 6-35. The player rolls 30, hitting the range. He then rolls 88, reducing the bonus to +36. Then the original Extremely Hard -35 is taken away, leaving just +1. Add the initial roll of 30 and you'll have +31, a Failure.
This explains how the skill challenges are still really challenging even with very high skills bonuses.
I've not only taken away. I've added several additional Success Levels beyond an Absolute Success. There's Remarkable Success (231-350), Heroic Success (351-500) and Legendary Success (500+). If someone hits these epic levels they have far greater advantage in conflicts or otherwise.
Combat
In combat we have several options taken from a different Rolemaster generations. We have Combat Stances, Combat Styles and so on. We have two different ways to follow the combat actions: First is our own Action Point system that is highly modified version of RMC IV version. Every action imaginable in combat takes an certain amount of Action Points. An attack may take 30AP's, loading a bow could take 12AP and casting a spell can take 100AP. When the encounter starts, we mark AP 0 and roll for Orientation that gives the exact AP when each combatant can start their first actions. Then we just count the AP's and progress ahead. After each action the player states next action and resolves the AP required. The usual fight last 200-300AP's but may take as long as 1000AP. At certain points Fatigue is rolled. This makes our combats highly tactical and very, very detailed. Since one AP is 0.25 seconds, 40AP's equals to 10 seconds (old "round"). Melee Fumbles are converted in our game from Runequest 3rd edition and are deadly. Ambush (we have sort of Melee Ambush option also) is very deadly. The tactical nature of our combat makes my players very wary when in such situations. They know that any arrow or spell shot from the dark can be deadly. 3rd or 4th opponent gets a free strike and with some luck two 3rd level orcs can make any character to fall down (Bull Rush or Collision Charge) and that's always bad. Any moment someone can fumble and the whole dynamics of the situation changes.
Fatigue and Encumbrance is the real enemy of a characters. Fatigue increases in "levels" like Winded-Tired-Exhausted-Delirious-Catatonic. Each Fatigue Level adds Action Points to every action (making them slower), gives negative bonuses to skills (in percentages), may cause Stress, increases Fumble Range and accumulates as long-term Fatigue that requires good rest (an usual camp will not do). Fatigue and the general well-being is in great role while travelling. The players find it challenging to get anywhere in totally good condition. It is normal that after a long day of walking in wilderness at least half of characters carry some negative modifiers. If they fail to find a very good camp site these modifiers will not heal at night and they start to accumulate dangerously. The players really, really much appreciate Inns and their own homes. Now imagine some long dungeon crawl where good rest is almost always impossible...after a three-day crawl even an basic cave troll family (normally just an inconvenience) can be fatal.
Magic
Now that has cause me really trouble as a GM. High Level Rolemaster Characters have easily hundreds of spells and they offer solutions for almost every possible situation. Where to start... I've allowed a high number of spell points but I require really tight premisses to get them back. In long and tight scenarios it is usual that our spell casters are out of spell points, even when they start with 400 or something. Casting of higher level spells take a lot of time making most of the high-level spells obsolete in a fast moving situations. Keyed Spells (Spell User's Companion) and Spell Stores give tactical options for characters. Spell Mastery is widely used: Spell User's can modify any spell almost infinitely at the cost of high power point consumption, slower casting and higher risk of failure. Normally we never have a situation when the spell is cast "Automatically". Usually it's a skill check and with it comes the risk. And our Spell Failure Table is very long, and very much feared by the players. Resistance Rolls are different than in any RM version - we have several options and tactics that make it possible for low-level magic users to get their spells through and the low-level creatures to get cover from the spells. Even our 80 level sorcerer cannot be sure if her spell is going to go through against an prepared opponent. It's highly tactical.
Power Perception rules make it easy to detect any spell casting happening nearby. This makes the spell casting in certain areas a risk.
I've taken an strict approach to certain powerful spells like Invisibility or Mass-spells. For example, any sudden movement will cancel Invisibility as will such things like drinking and taking a leak. Mass-spells require marking every intended target making it very slow and so on...Fireball against the wall of opponents takes an full effect only on the first row, as the second and further on rows will be well covered by their comrades. Against Elemental Spells the skills like Adrenal Spell Avoidance (RM2 Arms Companion) or Spell Deflection (RM2 Arms Companion) enrage my bloodthirsty players more often than not. Counter magic is far more powerful in our campaign than anywhere in the RM rule books I've seen.
Scenarios
Most my scenarios require a lot of role-playing. They also always add to the main campaign somehow. We don't take sidesteps so the interest keeps up no matter what type of scenario we play. Regardless of high levels we can play any type of scenario. Last scenario was an conversion of Warhammer FRPG "The Edge of the Night" that took place in our world. The scenario is meant for very inexperienced characters by itself but in my conversion the main opponent was an just-awakened son of evil Chaos God trying to take hold of the city and reach for higher position in the great Empire in our campaign. He was at 120 level but all he and the characters was tied by the sensitive social situation so there was almost no dice-rolling at all except for certain Social Awareness or Perception rolls. I keep up the interest by letting the characters keep up their own "to-do lists". My characters know the exact situation they are in the campaign. They make their own decisions of how to proceed as the champions of their kingdom and the heroes of their religious cults. Usually I ask what you are going to resolve next and once they got the discussion done I build the scenario around their aim or complete my notes around the topic. Last such scenario was when the characters finally got impatient about the important book they found years ago (around 2010 I think in our time). None could read it since it was written by one of the first dwarven sages to ever exists in our world. The characters had done some measures (pacts etc) in the past and they knew there was one dwarf who could read it. Unfortunately that dwarf was imprisoned in evil stronghold, at mountain-top monastery. They got to know that this monastery was build around 1500 years ago and totally protected from intruders. Everyone who was not totally embraced the evil ways of that race was going to get caught the moment they crossed the monastery walls. Players made an deal with higher powers, got their hands on one-time ritual of Time Travelling and got their-selves on the time when the monastery was being build. They got on the site and were taken as slaves. Their toiled some weeks, survived the harsh treatment and finally got sealed inside the walls as an sacrifice. Then they fell in 1500 year sleep that was possible due some spell the witch prepared earlier. They woke up, broke out from the ancient wall to some old dusty storage, did some role-playing and subterfuge as newly-arrived novices and finally got away with the dwarf without ever triggering the alarm because they were in the inside when the enhancement was created! What's inside the book will shift our campaign to a next level. Again, only fight in this scenario was (if a couple of assassinations are taken off) when the novices were grinding against each other in Martial Art sessions. And there was one great moment when our Sorceress fell in love with one of the evil cultists (she) who also left the monastery in the frantic escape and allied with the characters.
We do have also have fighting scenarios. We have War Law campaigns. We constantly play solo in email and Google Docs between the scenarios so we are prepared in table. The characters have full lives and roles in their kingdom. They have everyday lives and responsibilities they manage. We simulate together the kingdom in a detailed way (yearly budgets, farming etc). I write narratives around their off-line actions or of something that happens around them to show what was the result of their achievements. I try to make each scenario different. I have total of eight players so when it suits me, we almost always have the session. I require three players to attend at least, sometimes some situation requires an certain character to act so that may cause some calendar issues but generally I avoid such situations.
Thanks for your question, it was interesting to compile my thoughts on this.
If interested, I can tell more from any topic you wish.