Greed Island sucked. I dropped it in the middle of the bullshit training sequence once I saw the parts I probably shouldn't miss like the Phantm Troupes appearance in that arc
No, it's not skippable. It's worthy its reading. And why would not like concept? Do you just like the character being strong without almost any explanation behind it?
Also, I'd advise you to watch the anime rather than read the manga in the Chimera ants arc. It's pretty much the same thing as the manga, but with far better art and good soundtrack. Sometimes the manga art sucks.