Weirdly proportioned psionic humanoids, unsubtly imported from Dark Sun.
The obvious balance point here are goliaths (rated at +1, unlikely to change), and I gotta say that they compare quite well. Both are medium-sized, both get Powerful Build, both get +2 constitution and -2 dexterity in addition to a strength bonus (+4 for the goliath, +2 for the half-giant).
The few differences are quite minor. In addition to the strength bonus, half-giants get +2 on saving throws against fire/heat effects, two bonus power points, and Stomp 1/day. Goliaths, meanwhile, get +2 sense motive, tolerance of high altitudes, and bonuses when climbing and jumping. Half-giants have a minor niche in getting the giant type, which opens up Return To Nature shenanigans, but those are so niche that I'm comfortable dismissing them as a viable build.
All things considered, the half giant is a goliath that sacrifices some brute strength for psionic utility, and that's a fair choice. +1 LA for those guys.