From what I've heard this had to be changed because they wouldn't have been allowed to shoot with the sandals, but it's fairly minor to me.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.
Both of these are things that could have been kept truer with close to no effort, especially the Alvida scene.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 Cozy 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.
For the departure with the Marines saluting, they'd probably have to do some setup with showing Morgan being absolutely brutal as soon as something doesn't go his way, but that should have been possible at all.
There are more, like Usopp not having his moment of courage during his arc, which might actually be the worst offender.
That's the kind of stuff I really don't like in the show, but to me it's still a positive overall.
I've definitely seen other shows, be they original or adapted from different source material (basically all of it way easier to adapt) that ad worse first seasons.