How to accurately describe One Piece to someone that hasn't read it? It's hard as hell to it without getting fanboi'ish and stupid to a degree of over 9000!!!!!!!!!!!!!!!!!!!
The start may be a bit boring to some/most, but if you stick with it you won't regret it. Or you might, when you've turned into a an idiot addict like us others...

One Piece is one of the most original pieces of literature I've ever read, equal to, or surpassing Hiromu Arakawa (FMA), Nobuhiro Watsuki (Rurouni Kenshin), and Akira Toriyama (Dragonball). Oda's a genious at telling stories; he manages to pace the stories to match ADHD kids as well as those that're looking more in depth; he manages to do epic and serious stories - stories with deadly serious themes varying from slavery and abuse, to genocides and regicides - stories he juggles with hilarious characters and settings; he's one of the few mangaka's I've come across that, from day 1, has just kept getting better and better, never seeming to lose his touch, always reaching new heights; he's one of the few people that's been able to take a completely ridiculous concept (the devil fruits) and made it not only accepted, but also setting a standard for how to balance powers and abilities; and he's the only one I've read so far that's been able to juggle the old and boring "I have a dream"-character(s) without turning into bad cheese, shitty or just plain stupid; he's one of the few mangaka's out there that's been able to create a protagonist that's not only fucking awesome, but also one you cheer for regardless of situation; oh, and he's one of a few that's been able to create an entire cast of characters that're all equally awesome and delightful to focus on; he's one of a few mangaka's that's been able to write 500+ chapters in such a bizarre setting, characters and powers without getting dumb.
Obviously I failed, I crossed the 9000 threshold. Obviously those're facts according to a fanboi. Obviously, the manga's far from over. :>