I think nematodes have had much more successful evoltuion than humans. There are way much more nematodes in the world than humans, and they have been here aeons before humans and they’ll probably survive much longer than the whole human race.
Nematodes make humans look quite amateurs.
Also, I think squids are more successful than humans, because they can dive very deep without any diving apparatuses, but humans can not. And squids do not suffer from appendicitis or wisdom teeth.
Why did species other than humans fail to have a successful evolution?
I think this question comes from a misunderstanding of "success" in terms of evolution. Success may be measured as adaptation to one’s ecological niche. In such terms, every species is "a success." Dolphins are better swimmers than us, eagles are better fliers, etc. We could also look at the success of bacteria. They could be considered more successful than us based on: total biomass, number of individuals, number of species, number of ecolgical niches occupied, length of time on earth, etc. When it comes down to it, every species that is around today is a result of "successful" evolution.