Let me preface this by saying that I hope I don't come across as being too insulting to a couple of the people who were involved in Rolemaster/HARP in the past, and that this may be a little long as I tend to ramble too much (as mentioned below my writing skills still need some work and editing).
I come to this from kind of an odd point, as the first time I saw one of those hand-drawn black and white ads for Rolemaster back in Dragon Magazine in the early 80's it intrigued me, so as soon as the local gaming store owner made his first purchase to sell I was one of his first customers and had been a loyal RM fan ever since. I purchased just about every ICE product he carried in that store as well as many others after I moved away including MERP (Middle Earth Role Playing) and eventually Spacemaster when it came out. Had played D&D as well as AD&D for a few years prior, as well as Traveller, and a few others of the early RPG's; but Rolemaster/Spacemaster in my opinion were and still are the best system out there. The details, the flexibility, the customization options; it was the most realistic system out there and simulated how real-world weapons and armor interacted far better than anything else I had seen (the next best was the very first board/rpg game I ever played which was Magic Realm, which was still a hell of a lot better than D&D or AD&D or anything else). Maybe it is my engineering background and mindset that cause me to have such an opinion and to take that viewpoint, but that is the case in my opinion.
It just so happens that the originator of HARP (Tim Dugger) was a player in an email-based Rolemaster game that I ran for about 3-1/2 years back in the late 1990's. So when he came up with the idea for HARP I served as a sounding board for his ideas and suggested several of the aspects that went into the HARP mechanics even before he submitted his proposal for the system. I also ran one of the play-test groups that play-tested it somewhat extensively.
When he submitted the proposal for HARP, it was after the original ICE had filed for bankruptcy and the IP rights had been bought by the current owner, and licensed to Moljinor or something like that (which was being run by some of the previous managers that in my opinion hadn't done a very good job the first time around and continued to do a poor job the second time around under the supposedly "new management" that was only a thinning of the old management).
The goal with HARP was to create basically a game that was different than RM but had a similar feel while being simpler and easier for new players to learn, but at the same time having enough similarities to the various versions of D&D that the D&D crowd might be willing to give it a try. In that respect HARP was well done, but personally I still prefer Rolemaster due to its greater depth of detail. While HARP is closer to a "Simulation" of how an RPG mechanics system should work than most of the other RPG's on the market, it still is not as good as Rolemaster in my personal opinion. However it is still much better than most of the other systems out there on the market.
I think that the later version of Rolemaster (RMSS/FRP) was a definite improvement over the original version of Rolemaster, however I still own those original books and still reference and pull information out of them now and then. Likewise with Spacemaster, I liked the mechanics behind the later Spacemaster Privateers (which were based off of the later RMSS/FRP mechanics), but liked the earlier Imperium (sp??) setting for Rolemaster better than the Privateers setting, although the privateers setting was still better than a lot of the sci-fi settings I've seen in the RPG industry (again, only my personal opinion).
Likewise HARP SF was intended to be a sci-fi version of HARP in the same way that Spacemaster was the sci-fi version of Rolemaster (in both of its previous incarnations). When the concept was first discussed before Tim found a writer for it (which was Nicholas Caldwell, whom I'm happy was the chosen writer) with me, before it was even announced that they were thinking about it he and I had several discussions about it. Tim had even approached me about writing it prior to any mention to the public about such a product even being considered, but my writing skills are not that great and I don't think I could have done anywhere near as good of a job with such a massive project as what Nicholas did. And the concept that Tim had as the basis for the setting used a lot of my ideas and suggestions, even though I suspect Tim probably claimed most of my ideas as being his (as publicly I didn't get any more credit than as a play-tester for any of the HARP products), similar to how he had with HARP. ... Don't mean to sound bitter or anything as that is not my intention and I now realize that it might be sounding like that is the case, as that is not the case, as I am happy to have been able to contribute and be involved with the development process, after all as stated I still prefer Rolemaster/Spacemaster to HARP and HARP-SF. But I'd have to say that HARP and HARP SF would be in a toss-up with FUDGE as my second choice for both fantasy and sci-fi game mechanics.
But the setting that I use (and have been using and developing since the early 1980's) was very heavily influenced by Rolemaster and its level of realism and its mathematical simulation style of mechanics. If it were not for Rolemaster I probably would not have spent the thousands upon thousands of hours developing the setting/world that I've been pouring my soul into for the last 30 years.