Nelson was my intro to the world of Aliens comics so I'm biased, but I think his work is spectacular. It was moody and brooding. You're right about the way he draws the aliens but I've come around to appreciating the style.
I started reading the original Aliens series with issue 2. My only previous exposure was when I saw the Aliens film on my birthday. So I wasn't quite sure how the aliens were supposed to look like in detail. At first I really liked his portrayal, then with time I realized that he wasn't quite drawing them accurately, especially the ridges on their heads, but I've come around full circle. I just appreciate that he has his own unique style in drawing them. His aliens are totally distinguishable from any other artist's.