Shakespeare's contributions to the English language are so important to us today because he set precedent for new genre styles (especially for dramas, romances, and tragedies), later authors/poets, musicians, psychological theory, and language composition.
Shakespeare’s work was also important because during the Shakespearean era, the English Language was not as standardized as it is in the modern-day. Shakespeare influences styles of spelling, pronunciation, expressions, and punctuation.
Samuel Johnson, author of one of the first widely accepted English dictionary, “A Dictionary of the English Language” often cited Shakespeare in what became known as “Johnson’s Dictionary” (predecessor to the modern and widely used Oxford English Dictionary).