I'm pretty sympathetic to the length argument. I always balk at starting a new series because of length, usually for no good reason. I put off Gintama for a long time because of the 200 episode price tag, but am now 40 episodes in and loving it. And slightly related, I got a friend to watch One Piece by saying I would watch all 50 episodes of Gundam SEED. Six months later, I'm still on episode 29 and he's all caught up and reading the current manga chapters.
Regarding all those who have not seen Naruto or Bleach, I personally think the very initial arcs in both are excellent, creative, well thought-out, exciting stories. The problem with the both of them is that due to their success their writers have had to come up with ever-expanding story lines. Most people will be lucky if they ever have one good story in them in their life, so you can't blame Kishimoto or Kubo. We can't all be Oda-sensei and have more creativity than we know what to do with.
If any new Japanese people I meet are unfortunate enough to ask me what my hobbies are, I tell them I love One Piece and then try to get them to read it. Since most Japanese guys already read it, the line of reasoning I employ with girls is "本当に感動されちゃう、絶対に泣くよ". "You will honestly be moved, and you'll DEFINITELY cry." At which point, their friend who reads it (most people I meet here do) will chime in and mention something about Chopper and crying and my job is done.
For friends back home, I usually give them the genius line. There are very few creators who can live up to long-time expectations; they usually run out of ideas. Rowling created a wonderful world but never was able to stick to it's rules or continue to instill a sense of awe in her readers as the story went on. The same goes for Lucas, tho that's more a case of ebbing skill rather than story telling ability. But Oda-sensei, he doesn't seem to be running out of story ideas. In fact, he seems to be honing his story telling into something lighter, more compact, less trite, more ambitious. One Piece is the only story that is still getting better and better with each chapter, even after 13 years. How many other long-running stories can you say that about? I can only think of The Wire.
And I honestly love the first 25 episodes of One Piece. It has a childlike, fairy tale quality that Oda seemed to abandon for Dragonball-esque wonderousness once they entered the Grandline. I think if anyone really has any sense of what good story telling is, they will appreciate the anime from the start.