Not because it's bad. Quite the contrary, in fact; the artist is talented, if a bit enamored of loud colors. No, the pain, I believe comes from one poor decision that messes with everything.
The artist for McNeill's is Maine illustrator and painter Rob Logan, whose site is immediately identifiable with bright, almost neon colors, jarring images, and a sort of twisted cartoon style (though he needs to put fewer red letters on black background). If you've got a minute, go there and click on the puzzle for a pretty decent pictogram.
This piece by him I think is particularly strong:
As we'll see, though, that doesn't always come through at McNeill's.
The most mild of the McNeill's labels is for the Maibock:
What if I told you one small change would completely alter the way you see this label?
Let's do this again:
The point of this post is not to skewer McNeill's, which I'm sure is a nice brewery (I've had a few of their beers) that employs a capable artist. The point is reinforce that a seemingly tangential design decision - in this case, to employ radiating neon colors to make the beer stand out - can totally interfere with and even nullify good design decisions. Details matter, and, in my opinion, McNeill's is hurting themselves by not paying close enough attention to them.