Complex sentence: Critics have generally been unimpressed by it as a work of art, although the engraving has had a few defenders, and exponents of the Shakespeare authorship question have claimed to find coded messages within it.
Split into simpler sentences: Critics have generally been unimpressed by it as a work of art, though the engraving has had a few defenders. It has also been used by exponents of the Shakespeare authorship question, who have claimed to find coded messages within it.