Yeah, as the others said, if you know Rolemaster then HARP will be easy to pick up on the fly. It's close enough to an "RM Lite" that that's how I essentially look at it.
To put it very generically... it's sorta RM but...
The skill system is reduced in volume.
Attack and Crit tables are combined and bit more limited.
Spell purchasing is done by the specific spell that you can scale up rather than by list with various power levels of the same spell.
If you like RM, but you'd like it scaled back a bit, HARP is a great choice. (Not trying to sell you on it either... cause I actually prefer RM).