2. Smart coworkers (well before this came out)
3. Good compensation (I heard for top tier applicants, they give something like MSFT total comp as salary with a ridiculous amount of paper money)
4. Assumed less bureaucracy compared to Big Cos because of unicorn/start up status
5. Ability to develop the first X in the new ride sharing/autonomous car industry
Uber would be a good fit for someone who specifically wants to work at a big_unicorn with large scale technology problems.
Most engineers wouldn't be able to accurately evaluate the ability of the leadership of tech companies, so that negative is out the door.
For the ethics portion, that's subjective.
For the cut-throat nature of the company, I heard that it was worse than most tech companies but not terrible (60+ hr/wks) like some financial companies.