The Garp changes are the only real negative to me. He's so serious unlike manga Garp. And they're sort of making him a bad guy.
I disagree, as I think that's intentional, because to be honest, the meeting between Garp and Luffy for the first time in the manga, could have had WAY more tension involved.
Like Garp just showed up on Water 7, and everyone was like "OMG THE MARINES" and then a few panels later it was like "Oh, that's Luffy's Grandfather."
This way, it actually builds a lot of tension, and will hit MUCH harder for people when they finally get the reveal that this whole time Garp was Luffy's Grandfather, and not actually after him in a malicious way.
I think it works better as a "Gotcha Moment" than what the manga tried to achieve.