1) I have tried to read him a couple of times and didn't get far either time.
2) "The most important author of world literature since 1945" is one heck of a stretch. I would describe him as "an important, well-known, respected US author who is much admired in some literary circles."
I haven't looked at Wikipedia yet, but because of Wikipedia's editing process and the requirement for "verifiability" (citation of reliable sources), when Wikipedia expresses a judgement it is usually a good consensus mainstream judgement. Let's go see.
<em>Thomas Ruggles Pynchon Jr. (/ˈpɪntʃɒn/, commonly /-tʃən/; born May 8, 1937) is an American novelist. A MacArthur Fellow, he is noted for his dense and complex novels. His fiction and non-fiction writings encompass a vast array of subject matter, genres and themes, including history, music, science, and mathematics. For Gravity's Rainbow, Pynchon won the 1973 U.S. National Book Award for Fiction."</em>
So, no Nobel prize, no Pulitzer prize. An important contemporary author, whom I personally don't happen to find readable.
"Most important author of world literature since 1945" reminds me of people I knew in college who liked to insist that Anton Webern was the greatest composer in history, or that Marshall McLuhan was the greatest thinker of the twentieth century, or that Barnett Newman was the greatest artist.
I wonder who was the greatest <em>before</em> 1945?