I have collected a few more game manuals from old RPGs and am having a wonderful time reading through them... mostly laughing at the mechanics and the way old games are built, but occasionally being very impressed. In particular I found the Amber RPG (based off of the Chronicles of Amber books by Zelazny) to be fantasically written and executed though you really have to buy into the theory first off, and the theory is a bit deep.
The thing is, most of the numbers in an RPG are simply there to let the players interact in a random way with the obstacles put in front of them by the GM. The game doesn't feel exciting if there is no danger, and if the danger is entirely that the GM may just decide that you lose it doesn't feel much like a game. In a game where the GM cannot put *any* significant obstacle against you though that rule doesn't apply. Because Amber at its heart is a PVP game where invincible superheroes who can do absolutely anything given enough time duke it out amongst each other randomness really isn't necessary. All you need to know is who wins when players fight each other and a simple ranking system is good enough for that. Amber has amazing rules explanations and examples; far better than any other RPG I have ever read. It *needs* those examples because it has so few rules and it delivers. I don't intend to ever play it but I must give credit where it is due. If you want to play in the world of Amber, this RPG is perfect.
GURPS, on the other hand.... is a colossal mess. Sure, you can build a robot cowboy spaceman ninja psychic superhero with a phobia of six sided dice and only one eye, but then you have the challenge of actually figuring out how to do anything. The amount of work required to generate a character is serious and the tables you have to pick things from are intimidating. This is all not to mention the skills lists - I know a lot of gamers who would take one look at the skill lists and rules for related skills and throw up their hands in disgust. GURPS is a product of its time where RPGs were designed for hardcore nerds who revelled in system mastery and were unworried about recruitment. We're all hardcore nerds here, who wants anybody else?
Those days are fading rapidly. The time where you could build a good but ridiculously intricate and complicated RPG and just expect people to give up their current game to sink 30 hours into learning your new one are a thing of the past. Building games that way just ensures that people will stick to their old game because they just don't want to put in the time to learn a new one. Nobody cares how good GURPS is because everybody already knows DnD so DnD groups fill up quickly and GURPS games collapse because you can't convince the new guy to pick it up.
This is something I am struggling with in Heroes By Trade. I really wanted to have a complicated healing formula that took into account the skill level of the physician (if any), Constitution, a random roll, and potentially other factors. Of course nobody wants to figure all that crap out every single day just to see how fast they heal so I reduced it to a simple 1 healing a day normally, 2 if resting under good medical care. Easy to remember, easy to get into. I am reminded of the old DnD improvement my friends and I (mostly Sthenno) were making years ago. It was mechanically excellent but extremely complicated and when we saw how easy and straightforward 4th edition DnD was we abandoned it. Our system was much better than the mess that 3.5 DnD was because it was equally complicated but mechanically superior but no way were we going to convince people to swap to it over the straightforward but mechanically inferior 4th edition.
What people really want, I think, is an excellently written system that has a really simple set of rules and choices. Everything needs to be intuitive, fast to resolve, and extremely easy to explain. If we have to suffer under some 'unrealistic' rules or obvious simplifications that is fine; the goal is to get people roleplaying, not studying up for a final exam in Obscure Lists and Alternate Rules Interpretations 108.