Well, obviously (like everyone else said) no one really knows, but I have three opinions:
As a fair warning, two are not so good, the other is better:
First, as a 'humans are horrible' view point, I think that the world will be a large concrete and metal ball. People keep expanding, building roads and buildings and killing creatures just for the sake of land. I'm not really an extreme tree hugger, but I don't agree with taking advantage of a planet that gives us a home. Bbut, that's not what you asked for... Getting back on topic... I think it will be very much technology run, and I don't think you'd see people on the streets or anything like that. I think that people will have technology doing everything for them, getting groceries, watching/feeding/caring-for children, doing all household chores, fixing things that have broken down, and basically I believe that humans will be secluded into their homes, if not rooms. Oxygen will become a problem living on a planet covered in concrete, so I wouldn't be surprised if a government force supplied oxygen to households or soemthing like that. I've always kinda pictured a big concrete mess, with a single tree in a glass dome for air. Jobs and human labor, as well as crime and violence, will be nonexistent. At the same time, though, I think it would be a very lonely world, with barely any human to human interaction.
That was the worst outcome I came up with. My slightly better one is kind of an after effect of that: If the world were to be taken over like this, the Earth would surely, over the coarse of time with a worldly disaster or something like that, take back from the humans what the humans took from it: And that would be the forests and the animals and everything. So, I believe the world would look like a huge forest/desert/sea full of ruins and rusting wires and cables and metal. The concrete cracked, the glass shattered, major buildings that once were, destroyed to rubble. I think humans would live among the wreckage, if they could, and I think times would be harsh. Nothing like the dull luxury one would have in my first hypothesis. Anyways, the race of humans would basically be like refugees, living in a world of... I don't really want to say chaos, but hard times. The creatures would be different, too. Since all the original lions and tigers and bears were wiped out by the humans earlier, new creatures rise from the ashes. But again, I have an over-active imagination sometimes... Heheh... O.O
Thirdly, the one that I really wish will be: A world where humans realize that though the may be the smartest creature, they do not have the right to rule over the entire world like greedy savages. That they learn when to stop, and that man and beast have equal life, no matter what species you are. Not saying we'll all be vegetarians, but what we take from them we must also give back. Kinda the 'All energy is borrowed' scheme from Avatar, only, everything is borrowed. When you take something, like the life of a cow for your meat, you must also give food and water and shelter to another. No animal farms and zoos and things that gloat human supremacy. Make people work for it a little =) But most importantly, I think that the world needs and hopefully will have Respect for all things living by the year 3000. After all, we are all earthlings.
Hope this wasn't an overload! I didn't think I would write so much O.O ...sry...