Well, the only voice in the game I didn't like was Maggie's. Like VampireNaomi said, it was always using the same tone. For example, when she says "Cutting Brink's hand would be terrible" (or something similar), it's like she's ordering a pizza or something
. This was specially "shocking" for me because the first time I played the game, it was the Spanish version with Spanish voices, and Maggie's Spanish voice is so much "reflexive" and "profound"... so I was a bit dissapointed when I played the English version.
I liked Low's and Brink's voices, but I agree with you: they still can be much better. The problem is that it seems like the actors didn't know very well what was happening in the screen.
I think The Dig is the only LucasArts adventure where I prefer the Spanish voices and acting instead of the original version. Anyway, I don't think the voice acting was BAD, it could be better but not bad at all for the time the game appeared.