Fuzion Core Rules (at least, the last official version of the rules, which was 5.02), inherited rules from two sources: the Hero System (by Hero Games), and the Interlock System (by R. Talsorian). This ruleset owes much to both, and there was even a conversion system with some designer's comments on the rules decisions.
And I was a fan of both. Interestingly, I was more of a Hero System fan than an Interlock System fan BUT, I loved the settings that R. Talsorian came up with. The parallels between the systems were interesting, but I found that the most interesting things for me in the system were some of the ways they handled damage.
As far as damage is concerned, it's split into two types of "hit points": Stun and Hits.
Stun is the amount of stunning damage you can take before being knocked unconscious.
Hits are the amount of killing damage you can take before you start dying.
Both are x5 multiplier on another Primary Stat, quite different from another lesser "damage stat" called Resistance which is based on a x3 multiplier.
Aside from that, on the basic level, it's not much different from hit points mechanics-wise.
Why do I like it? Well, I've always liked this damage philosophy from the early Champions / Hero System days, because at some point I became dissatisfied with hit points and some different mechanic for handling knocking someone out (Gasp! Blasphemy!) and the whole percentile system for assassination.
I realized at that age I was looking for a game system that somehow hewed closer to my limited understanding of combat physics. Now while I couldn't really handle Phoenix Command / Living Steel / Stalking The Night Fantastic rules (too complicated), the AD&D and then AD&D 2nd Ed rules abstractions seemed to run counter to my tastes.
Fuzion follows the philosophy that armor should reduce damage, as well as the philosophy that there is inherent toughness that reduces damage -- as opposed to the D&D philosophy that it be bundled with the To Hit resolution.
Stun Defense reduces stun damage. Formula is Stun damage minus Stun Defense equals Stun taken.
Killing Defense reduces killing damage. Formula is Killing damage minus Killing Defense equals Hits taken (well, they didn't use Kills because that's reserved for high level megadamage as per Mekton -- an Interlock game for giant robots).
I also like this, because I appreciate the way you can differentiate creatures that can be super-tough vs. punches and kicks yet totally defenseless against guns -- while other creatures can bounce bullets but not rocket launchers and so on.
Fuzion also brings in the concept of damage statuses from Hero:
- take more than 1/2 Stun from a single attack, and you're Stunned -- lose your next Action;
- take more than 1/2 Hits, and you're Impaired -- take a penalty to your Primary Attributes.
And there's the concept of damage rollover from each type of damage into the other:
- for every 5 points of Stun taken, take 1 point of Hits damage;
- for every 5 points of Hits taken, take 1 point of Stun damage.
The logic is plausible, and is a bit more simplified than same concept in the Hero System.
I also enjoy these in the game, because they add some interesting combat texture and tactical concerns for the player. Plus the plausibility helps reinforce that sort of "action movie" logic for an RPG.
Overall, I liked these rules elements, though I feel that the rules could have been written more consistently and clearly.