A detailed analysis of some rules that, at first blush, might seem a little wonky but are actually okay.
The Compendium I contains some guidelines for making your own advantages and disadvantages. Along the way, they give the "formulas" for how points values should be totalled. However, it can sometimes seem strange to see that a seemingly opposite adv / disad pair don't cost / give the same number of points. Likewise, it can seem odd sometimes to find two or more advantages that all cost the same amount but some have special bonuses while others don't. This can seem perplexing, but one's understanding is greatly aided by understanding how point values are assigned to different traits. The rec.games.frp.gurps FAQ has this to say:
* How are character point values rated and used?
According to GURPS' line editor Sean Punch: Attribute levels and advantages (including Unusual Backgrounds, positive or "negative") are priced according to their RARITY, skills are priced solely on their DIFFICULTY and disads are priced for the INCONVENIENCE they cause. The "points" that are used to rate rarity, difficulty or inconvenience are the "natural" units for each of these elements. ... it should be noted that rarity and power (commonly called "usefulness") tend to overlap: it is useful to be a fencing master, but it is also quite rare.
Character creation is not an exercise in accounting.
>From Steffan O'Sullivan: Don't make characters for point efficiency. Make them for a character concept.
The "rarity / difficulty / inconvenience" guidline is a useful one and is a great help to understanding how things are priced. This immediately explains why, to give a few examples, Combat Reflexes is priced so low when it gives so many bonuses (it is not uncommon for characters to be experienced with combat), why Appreciate Beauty is a Mental / Hard skill (even though it's pretty useless), and why Dependents give so many points (they're very inconvenient).
The GURPS Frequently Asked Questions pages are also very helpful for clarifying how some rules work.
Krommnotes.org contains an exhaustive listing of many of the rules clarifications posted by Sean "Dr. Kromm" Punch to the GURPSnet mailing list.
Clarifications on Advantages, Disadvantages, and Skills (the 4th edition clarifications are right here "...Rulings on GURPS originally posted to electronic discussion forums, newsgroups, and mailing lists by Sean "Dr. Kromm" Punch." A truly excellent clarifications page.
New players are often surprised to see that while Strong Will is priced at just 4, Weak Will is priced at -8. These prices are correct; here's why:
Following the "advantages priced based on rarity" guideline, we can see why Strong Will would be priced at just 4; it is not rare for a heroic character to have a Strong Will. After all, the Good Guy can be interrogated by the Baddies but not crack. The Good Guy will race through a burning house to rescue a child, and he might grimace under the pain, but he won't turn back. And the Good Guy might be attacked by the Evil Doctor Mind Bender, but he won't allow the Evil Doctor to penetrate his mind. Hence, Strong Will is rightly priced at 4.
Weak Will, however, is extremely detrimental. Based on the "disadvantages priced based on inconvenience" guideline, Weak Will should be worth at least -8 points. Here is a (non-exhaustive but hopefully thorough) listing of all the inconveniences Weak Will carries:
The sum total of these nuisances is enough to justify the -8 points.
The alert reader might rightly point out that Strong Will applies to all of the items listed above. A poignant observation, but the Strong Will advantage and the Weak Will disadvantage are not nearly as symetric as they first appear. Consider: Strong Will can help you succeed at Will rolls, thus it cannot actually "gain" you anything it can only help you to remain at your current state. Weak Will, on the other hand, makes you more inclined to fail Will rolls, which in turn makes you more inclined to gain new disadvantages -- both mental and physical, as a result of failing Fright Checks or Crippling Injury rolls. If the two were actually symetric, Strong Will would make it possible for you to gain new advantages or Weak Will would not make it possible for you to gain new disadvantages. Thus we see, that just as the case at the ski lodge where you have young women looking for husbands and husbands looking for young women, the situation is not as symetric as it would seem.
And another thing: No sane person would ever take Weak Will.
For further enlightenment, see How does Will work? from the GURPS FAQ.
Voice is a 10 point advantage that gives +2 to reaction and +2 to six skills (some social, some artistic). It would seem at first blush, that Voice is a much better deal than two levels of Charisma, which would also give a +2 to reaction but no bonuses to skills. This analysis doesn't quite tell the whole story.
The base cost of 10 for Voice makes sense (5 ponts per +1 reac), but it has a built-in limitation: it only applies to people who can hear your voice. (This was explained in an email correspondence with Kevin at SJ Games.)
The following is a list of some of the occasions when the bonuses from voice wouldn't come into play:
For all of the above situations, Charisma would offer bonuses while voice does not. Remember that next time you have a sore throat, you're underwater, or you're taking a spacewalk. :-)
Thus, voice has a minor limitation that reduces the cost by about 20% or -2 (bringing it down to 8). To offset that, it has a minor enhancement that gives a +2 bonus to six social & artistic skills. This minor enhancement is also worth about 20% of the base cost, bringing it back up to 10.
For it's part, Charisma has the following things going for it:
For the sake of completeness, it's worth noting that a good Appearance (Attractive, Handsome, etc.) has a number of limitations, similar to those of Voice but it does not have a reduced cost. The tradeoff is this: they don't have to hear you, they just need to see you to be impressed. Consider that the next time you're in a foreign land where you don't speak the language.
Conclusion: I suppose TPTB could have just made a single advantage that gives positive reaction modifiers and a single disadvantage that gives negative reaction modifiers, but I think they wanted to mix it up a bit so they made a whole slew of 'em, each with their own special tweaks. Like it says in the quote above: "Don't make characters for point efficiency. Make them for a character concept."
This was explained very thoroughly in Roleplayer #8: GURPS talk. (Scroll about 1/3 of the way down.) There's a lot of other good stuff in this page, too.