As I understand it (parody RPG elements notwithstanding) HM was originally (and appropriately) based on 1e/2e and is actually playable (as much as those games were. I imagine enthusiasts of those games might prefer the originals for historical authenticity, but HM sounds entertaining and fun! And a sort of 2.6e, which is interesting (much as PathFinder 1 was a sort of 3.6.)
Hmm, according to wikipedia Hackmaster 5 was rewritten and is a "serious" game - which sounds like much less fun, even if it is more playable!
Hmm, according to wikipedia Hackmaster 5 was rewritten and is a "serious" game - which sounds like much less fun, even if it is more playable!