Half-giants are goliaths by RAW. But true Athasian half-giants don’t look a lot like goliaths.
Half-giants look more like this:
More like this:
than…actually, no, this is pretty good:
Here are some more pictures of half-giants:
For reference, here’s an actual giant. They’re huge. That island in the background isn’t as far away as it looks…
4e half-giants aren’t anywhere near as big as those in the pictures, of course. And if you want your half-giant character to look more like a goliath than the half-giants in these pictures, that’s fine. There’s plenty of variation. But the big bulgy half-giant is probably more common than the kind that looks like a large, buff human.