What is the best word for saying that Hamlet has left a GREAT IMPACT on modern English literature? Any word other than 'IMPACT'?
I don't like the term "impact" and always try not to use it, though that comes down more to personal preference than anything else. It seems to me that you are describing Hamlet's legacy in English literature. Perhaps you could use that word instead.
Some synonyms ofimpactare causatum, aftereffect, chain reaction, outcome, pay-off, results (Roget's Thesaurus).None of these, though synonymous, are as clear-cut and suitable as "impact" because each has specialized usage and differing connotations (i.e., inferred meaning). Some synonyms of effectare: consequence, repercussion, development, conclusion (Roget's). Again, none of these, including effect, have as good a relationship to your original intention as impactitself does. The definition ofimpactis that it is an influence; an impinging force. Perhapsinfluenceorimpinging forcemight serve your purpose well.
You could also talk about Hamlet inspiring other writers, or impacting/shaping the evolution of literature. 'Impact' has this connotation of leaving a lasting mark; but Hamlet's contributions could also be addressed instead of impact.
You could also talk about how Hamlet has "shaped" English literature. Certainly it has been influential in shaping or "dictating" the development of literature. Some of the answer to your question will depend upon whether you are searching for a noun or a verb to use - "impact" is a noun. If it is critical that you find another noun to use, you could state that Hamlet has affected the shape of modern English literature.
Maybe you could rephrase your idea to write about the "legacy" of Hamlet, which is far-reaching in literature. Legacy is somewhat similar to "impact" in this case.
So you want a word other than "impact?" The previous answer suggested "effect." That would work. You could also use the word "influence." Or you can talk about specific impacts. You can say Hamlethas changed modern English literature by..."
What about "Hamlet's effects on modern English literature are undefinable"? Hamlet's impact (or effects) revereberate throughout modern English literature?
You could even say Shakespeare transformed English literature. Harold Bloom says Shakespeare invented the modern human -- that he invented our concepts of character and personality -- so that can be considered a transformation.