I like it, but ... two questions.

First, Isn't a DC 11 will save somewhat low for a CR 8 monster? The usual formula of half its' hit dice plus its charisma modifier would put it at a DC 16 or 17.

And second... I don't know, it sounds to me like it makes a much better Monstrous Humanoid than Giant. Too many qualities that are ... out there. Veinburst being the most 'monstrous' of the abilities, but most of its SA and SQ are a little outside the normal realm of giantdom; taken all together and it's much more of a monstrous creature. Flavor text also would factor into my decision.