This thread is already on the way to becoming a Miss Universe competition...
"I want world peace, and I want everyone to be happy, and... and... no deaths!"
And not to bash anyone, but... I'd hate to be in a world where everyoen was happy, there were no deaths, and no illness, or any pain. Because without pain, sadness etc. we wouldn't even know the meaning of hapiness etc. You can't feel happy unless you don't know the meaning of the opposite, since you'd always take happiness for granted. And thus, it would defeat the whole meaning of it.
If everyone was nice all the time, you wouldn't think about it, since you'd never know anything else. And thus, it would defeat the whole purpose of the change anyway.
If there were no disease, illness, or death, we would lose out on a lot on other feelings aswell, and not to mention the fact that the world would be so over-populated that we wouldn't be able to stand up anyway.
So personally, I wouldn't change a thing. Although I might have made it so that I, and only me alone, could get anything I want, any time I want, including teleportation skills so I could get to and from any place I want in an instant

Because if everyoen had that ability, what would be the meaning of it? ;p