HJO3's House Rules for GURPS 4th Edition

Initiative. Each character will have an "Base Initiative" (BI) stat which is equal to the sum of their Basic Speed and any initiative bonuses (like the +1 from Combat Reflexes) multiplied by four. To determine a character's initiative, roll 2d and add the character's BI. Combat proceeds in order of these values with the highest number going first. Initiative is re-rolled every ten rounds.

Any character who gets snake-eyes on the 2d roll goes last, regardless of what their total initiative would have been. Likewise, anyone who rolls a 12 goes first regardless of total. If two or more characters get the same maximum/minimum roll, order is determined by a comparison of their BIs (if these match, have a quick contest of DX between the two).

Initiative = BI + 2d
BI = (Basic Speed + Initiative Bonuses) × 4

Buying Success. The "Buying Success" part of the Influencing Success Rolls optional rule on B347 is used with the following caveat: critical successes may never be purchased with character points. Also, if a player is going to "buy success," he/she must announce it immediately after the failed roll. (You can't wait to hear the effects of a failure and then change things retroactively!) Bought successes are assumed to have a margin of success of 0.

Used Optional Rules. I use the following optional rules: Optional Jumping Rules (B352), Changing Posture in Armor (B395), Bleeding (B420), Accumulated Wounds (B420), Last Wounds (B420), Malfunction (B279), Modifying Dice + Adds (B269).

Deceptive Attacks with Thrown Weapons. You can make a Deceptive Attack (B369-370) with a thrown weapon, but you're at -3 (rather than -2) for each -1 you want to applied to your target's active defenses for that attack. This is for thrown weapons only; Bows, Crossbows, and Slings can't use Deceptive Attacks (though special ammunition may be available that works the same way). [Credit goes to Ze'Manel Cunha on the SJG Forums for the original idea this rule's based on.]

Luther's Weak IQ Option. This house rule adjusts the cost of unbundled IQ to control min-maxing, make Talents properly worthwhile, give intelligent characters more realistic Will/Per, and normalize its cost when compared to unbundled DX. Basically, you can buy Will and Per up and down for 5 points/level like normal, but their basic levels are calculated thusly (rather than being flatly equal to IQ):

Will = (IQ ÷ 2) + 5 (rounded up)
Per = (IQ ÷ 2) + 5 (rounded down)

This gives unbundled IQ a cost of 15 instead of 10. Here's a table that shows the Will and Per levels at various IQs:
IQ
Will
Per
2
6
6
3
7
6
4
7
7
5
8
7
6
8
8
7
9
8
8
9
9
9
10
9
10
10
10
11
11
10
12
11
11
13
12
11
14
12
12
15
13
12
16
13
13
17
14
13
18
14
14
19
15
14
20
15
15
[This rule is taken directly from Luther's original WIO post on the SJG Forums.]

Character Background Awards. If you write a background for your character (preferably submitted before it/he/she enters play), I'll award you 1 to 5 points or more. The background should be at least one paragraph and written in past tense third person. Details you don't cover in your background may be filled in by your GM (Never mentioned whether you had any siblings? Guess what! Your twin brother needs a kidney transplant.).

"Be wary of the man who urges an action in which he himself incurs no risk." — Joaquin Setanti