Artwork is a mass noun, but it denotes two different types of mass.

In example 1, it denotes the mass of work that has gone into creating a single piece of art, so the comment is actually indicating one should look at the work that has gone into creating said art. This makes sense, because one can see the results of said work, and it is presumed that it is representative of that effort.

Artwork also means "a collection of art", because it refers to all of the work that went into creating it, so looking at a gallery of art, one could say "look at all that artwork!" and be correct.

For further definitions of Artwork: http://www.thefreedictionary.com/artwork