I was always curious about Hybrid Heaven because it was an action RPG on a system dear to me which lacked such kind of games.
Said that this Konami RPG for N64 is very unorthodox and kind of progressive in some aspects.
The exploration portion resemble more a third person action game than a RPG from the era, there is very little NPC interaction and the story is exposed very linearly (there are a total of 11 stages).
About the story it's kind of B movie story like Metal Gear Solid, just with an alien twist, it's serviceable if a bit dumb.
The whole game is set underground and the environments can be a bit repetitive and scarce in details (be prepare to travel through many corridors).
What I found very interesting is the battle system and the growth system.
Basically the battles are all real time, you can move freely the main character in the room and when your stamina bar(s) refill you can do an action which is menu driven but is influenced on yours and your enemy position.
The combat is also mainly done without weapons (just bare hands) and there is a big variety of moves which makes the game close to a wrestling simulation (menu driven!).
Also each part of the body react in different ways to strikes, you can stun the enemy if you hit his head or slow him down if you kick his legs and so on.
The upgrade system is similarly innovative and it takes a cue from Final Fantasy 2 that is each time you do a specific action you increase the relative statistic and when you suffer a new techniques from an enemy you can learn it.
There is also a class system but it's invisible and tied to your actions just as explained above:
Use mainly kicks and you become a kickboxer, use mainly punches and you become a boxer or use the grapples to be a wrestler.
It's very well thought system and more deep than I described (combos, hidden finishing moves, multiple stamina bars).
What is cool is that all these features are also valid for enemies which are well characterized through their fighting styles (there are the ones that are fast but weak, slow but strong, expert on grapples, kicks or punches, with special moves. See image below).
The game focus on the original combat system and make the whole experience a bit repetitive at times mostly due to the bland level design in the third person exploration part but the sheer originality of it is also what makes Hybrid Heaven a good pick for retrogamers who value games that may not be great but have done something that standout and was never really matched elsewhere afterwards.
Hardcore Gaming 101 article which expose well why this game is still notable despite the flaws:
http://www.hardcoregaming101.net/hybridheaven/hybridheaven.htm
Japanese trailer:
https://www.youtube.com/watch?v=fA45ATFGqMs
Funny TV commercial:
https://www.youtube.com/watch?v=D1ZcJLAEkdU
Image from the manual with the description of few enemies:
Hitting specific body part cause different effects which makes the battles deeper and more strategic.
Also the damage you inflict or take depend on the position in relation to the enemy.
One of the EGM snippet review which succinctly describe well Hybrid Heaven:
