I've only seen a snippet of it but haven't watched it yet. From what I've seen so far, though, there are a few things I don't like. I mean, it's not that bad at all as a live action, but it's incomparable to the OG material.
First of all, Luffy's wearing boots? What? Boots really ruin the image of a carefree dude Luffy is. They don't match well with the rest of his costume at all.
Then there's the Alvida scene. In the original, Koby is supposed to finally muster up his courage at the end of his arc and ready to die at any moment despite being scared to death. He's supposed to have been inspired by Luffy's resolve at that point. The live action has the same moment... at first, but then when Alvida gets pissed, he reverts back to being a coward again. It ruins the impact, man.
Another thing I don't like is that they cut out the scene where Koby says goodbye to Luffy and Zoro. In the original, the marines salute the Straw Hat, thanking them for saving their town from Morgan's oppression. It's one of the moving scenes at the beginning of the story that makes a lot of impact.
What makes me really mad, though, is Garp. They did Garp dirty. I'm not talking about the fact that Garp and Luffy meet in the East Blue when they're supposed to meet at Water 7; I'm talking about Garp's personality and portrayal. In the original, Garp is strict for sure, but he looks like a rough, badass, a bit eccentric grandpa who cares a lot about his grandson. In the live action, he looks like a grumpy old man with an anger issue. The scene where he laughs at Luffy makes him look mad instead of eccentric. Garp is supposed to be a chill dude, basically an older version of Luffy, but the live action has him look like an angry old man.