I love these stories. I much prefer the original artwork by Stephen Gammell. It is nostalgic, plus I feel like the artwork and stories belong together. The stories are not the same without the original art. That being said, there is nothing wrong with the updated art by Brett Helquist; it isn't bad, just I have no idea why they would even change the art in the first place.
If I were to run across Brett Helquist's artwork somewhere else and they were not tied to this books and my childhood nostalgia, I would really like them quite a lot. I am interested in his work and would read other books he does the artwork for. In fact, I love the art in A Series of Unfortunate Events.
Original Covers & Art
Updated Covers & Art
Comparison of their art style: Stephen verses Brett
As you can see, both are very good, but people who grew up with the original might agree with me in saying Stephen's is much more frightening and belongs with the text.