Watched about 50 episodes and I can see the potential. ''Old'' animation doesnt bother me at all, its more than fine imo.
Seems like it starts slow but I think just like Naruto, its all about the build up around characters and awesome fights/techniques and I can see this happening in OP, hence the potential mentioned.
I could see how ninja fights were cool before watching Naruto, but I was kinda sceptical about the pirate thing in OP. Down the line, there are swords fights, some people with unique technique (comparable to the kekkei genkai in Naruto), some characters with brute strength and others who are more cunning, melee or range, etc. The main character has an explicit goal to achieve, which he keeps repeating, and is pretty stupid/innocent/one track minded, just Like Naruto. Not to mention Luffy has a nice talk no jutsu too

Give it a try, I think its worth it.