I hate to seem to be defending those people criticising the art style before they've even seen it in a developed state, but that argument doesn't really hold water here. The reason low-res games could get away with having limited expressions is because the detail was low enough for the mind to fill in the blanks. When resolution gets higher, the artists have to work harder to make it seem expressive, which is why the Curse of Monkey Island characters had a range of basic expressions, and so on. If the original Monkey Island had been a high res game, they would have done more with those character animations - which is part of what makes the Special Editions feel a little empty in places.
That said, it's not all about facial expressions. Grim Fandango's skeletons could only do a limited amount with them, but the great use of body language especially in the cutscenes (seriously, watch them again!) really made up for it. So there are a whole raft of things that DF can and will do to bring the characters to life, from various facial expressions to animation stuff to voice acting and clever writing. Since we haven't seen how any of this stuff will develop yet - all we have to go on is a basic lighting and parallax scrolling test - it's too early to know exactly how these characters will express themselves on screen.
There might be some truth to it, I think Tim himself said the same thing about the special edition, I thought a lot of it looked rushed or low quality and that was most likely due to the budget. I think they did a marvelous job with monkey island 2 SE, I assume the success of the first one had something to do with it but unlike the first one, I played almost entirely with the new art, switching back and forth for nostalgia's sake.