I don't know the first edition, but I seem to remember having heard that they did mostly cleanup work - though a lot of it. Like making character generation balanced by default, re-doing all the core supplements like College of Magics. The gameplay itself probably hasn't changed significantly.
I kind of like leafing through HARP because it makes me nostalgic and has a few nice twists for the classic fantasy races (like peaceful orcs, sorry, Gryx, Halfling wanderlust, and I think some nice twists on dwarven beards), but overall, it always seemed like an RPG that doesn't quite know what it wants to be to me. Parts of it a nearly Rolemaster-complex, and in comparision, others feel simplistic - and not a lot is gained by boiling the damage table down to just the crit table (looking up crits separetely was really never the problem in MERP or RM), and some variety and fun lost.
The Folkways supplement is nice, though; it has a lot of general (and good) advice on building fantasy cultures. It's stuck a little bit between that, being a HARP rules supplement and also a setting supplement for both Shadow World and Cyradon, so there will always be big parts you won't be using, whatever you want out of it, but is still good. There's a HARP supplement on Religion in RPGs by the same author, but I don't have it - if it's of the same quality, it's certainly worthwhile.
And if they finally manage to get an expended Cyradon out, I'll definitely be on board, because it's a REALLY cool setting that went totally unappreciated in its time.
