It might sound harsh, but it's the truth: Harry Greener is a failure in every way possible. Although he realizes this deep down, that doesn't stop him from trying to convince Tod hat he once came within reach of stardom.
For instance, Harry frequently tries to frame his failures as successes. Back in the day, he had tried "to get a job by inserting a small advertisement in Variety," manipulating a reviewer's quote to make their negative comment seem positive (6.15). This is actually a pretty common technique in the movie biz. Regardless, the fact that Harry is still trying to pass this off as true evento Tod makes the whole thing seem rather sad.
In a way, the distinction between Harry the person and Harry the performer has completely evaporated. This is alluded to when Tod "noticed that Harry, like many actors, had very little back or top to his head" making it seem "like a mask" (15.12). In other words, he's worn so many masks in his life that you can't see his real face anymore. Similarly, Harry's mental breakdown in Homer's apartment—half-vaudevillian slapstick and half catastrophic seizure—shows just how jumbled he has become.
Ultimately, like everything else in the novel, Harry's death is an anticlimax—it happens off-page and provides no closure for his character. But maybe that's the point. Although Harry might have built himself up to be a legend in his own mind, the sad reality is that he was just an old man with unfulfilled dreams—just one more of those "people who come to California to die."