It was a good fun for purely nostalgia sakes. Luffy's ah~ was adorable!
But the characters had been altered quite a bit... especially luffy. We see him being a damsel in distress atleast 3 whole times! Drowning, knocked over, needing to double-team with Zoro for a minor villain like axe-hand Morgan...
But LUFFY giving advice was the most hilarious part of it. Any one piece fan would know he just doesn't have the maturity for it(in a good way).
But the final 2-min fight with Arlong blew me away.
So for that final fight and the fact that the show setting was quite beautiful, I give it a 3. If it wasn't for completely downgrading Luffy's character I would have rated it higher.