I was devoting all of my gaming energies to High Adventure Role Playing.
HARP has a few significant departures from its Rolemaster ancestry - especially Fate points as a core mechanic, and its XP rules.
But at it's heart it is still RM-style sim-oriented PC building and ultra-sim action resolution. So very different from 4e!
When our group started 4e, it was actually a merger of two groups: one had just fiished a 10+ year RM campaign (which itself had been proceeded by an 8+ year RM campaign) and the other had just finished a 3E campaign. I had actually been expecting to move from RM to HARP as our next campaign, but 4e intervened: I was excited during the lead-up, and very keen to give it a go once it came out and our other campaigns finished.
Before the 4e game started I sent around an email which included the following description of the difference in ethos between (on the one hand) RM and (much of) 3E, and (on the other hand) 4e:
Relationship Between Game Mechanics and Gameworld
Unlike 3E or Rolemaster, a lot of the 4e mechanics work best if they are not treated as a literal model of what is going on in the gameworld. So keep in mind that the main thing the mechanics tell you is what, mechanically, you can have your PC do. What your PC’s actions actually mean in the gameworld is up to you to decide (in collaboration with the GM and the other players at the table).
Some corollaries of this:
Character Levels
Levels for PCs, for NPCs and for monsters set the mechanical parameters for encounters. They don’t necessarily have any determinate meaning in the gameworld (eg in some encounters a given NPC might be implemented as an elite monster, and in other encounters – when the PCs are higher level – as a minion). As your PC gains levels, you certainly open up more character build space (more options for powers, more feats, etc). The only definite effect in the gameworld, however, is taking your paragon path and realising your epic destiny. How to handle the rest of it – is your PC becoming tougher, or more lucky, or not changing much at all in power level relative to the rest of the gameworld – is something that will have to come out in the course of play as the story of your PC unfolds.
PC Rebuilding
The rules for retraining, swapping in new powers, background feats etc, don’t have to be interpreted as literally meaning that your PC has forgotten how to do things or suddenly learned something new. Feel free to treat this as just emphasising a different aspect of your PC that was always there, but hadn’t yet come up in the course of play.
Skill Checks and Power Usage
When you make a skill check (especially in a skill challenge), use a feature or power, take the second wind action, etc, the onus is on you to explain how what you are attempting works in the gameworld. (Where a feature or power has flavour text you may use that flavour text or come up with your own.) Feel free to be dramatic.
Inadequate explanation which leaves everyone at the table scratching their heads as to what is going on in the gameworld may lead to a -2 penalty, or even automatic failure of the attempted action, depending on the circumstances.