I remember when I first started watching OP. The first 40 or so episodes were... well, boring, but after that it hooks you.
Like many others before me have said OP does suffer from filleritis(which long anime does not?) but not in the degree of Naruto. The concept of OP makes it difficult to have 1-2 ep-long fillers (except in the Logue Town arc and a few others), but that doesn't mean OP fillers suck. Although they are non-canon they do share most of the OP feel that canon episodes have.
Movies are non-canon as well, sometimes (most of the time?) even more than fillers (a good example would be Movie #7). However, movies have stronger supporting characters than fillers, IMHO. They do seem to have a (bad?) habit of being repetitive, but they're great nonetheless.
The biggest pro of OP is the character design. Each crew member has depth and emotion beyond that of Naruto. At around the time we see a new crew member (who is totally oblivious of that) Oda throws in a flash back scene from that characters past. These flash backs can be gruesome, tear-jerking, depressing and many others but always touching. We get not only to know the character but also understand them, their motives, their past and most of all their dreams, the things that make and keep them going.
In contrast to the heavy themes OP can be outstandingly hilarious. Every crew member has a serious mode and a funny mode (which, in some cases, is the lack of it). Luffy is an extremely funny guy (and I do mean chopsticks-in-his-nostrils ab-cramping funny), but damn, he's downright scary when he's serious.
Like all anime, One Piece can't be explained, it needs and deserves to be seen (or read). I once started anime watching as a Narutard, but slowly turned into a bona fide OPtard. And I wouldn't like it any other way. My advice is, start with just reading the manga, get to know it, and then, when you're around the AP arc (=Arlong Park) switch to anime. Use the aforementioned episode guide to avoid fillers (optional). Become an OPtard. It is your destiny.
No, seriously, do it.