#1 - Politics - Since the bar is so high at Uber, being smart and hardworking is not enough. You must be incredibly good at office politics to be successful - and in fact, if you are not good at politics, you can expect to be routinely passed on for projects and given low performance.
#2 - Performance Policy - Stack ranking is a disaster as teams are compared against each other although they have very different KPIs. Additionally, some orgs have little control of the outcomes of their projects, but are judged by results rather than contribution. If everyone is good, some people still have to get low marks, where politics is particularly prominent.
#3 - Work/Life Balance / Stress - Working at Uber is extremely stressful. Every decision you want to make is challenged thoroughly and rigorously and there are constantly people that are "toe-stepping" on you to ensure the best decision is made. While this is great for the company, on an individual level, it leads to very stressful situations where you must constantly prove everything you do and justify it.
#4 - People Last Mentality - The company makes no secret from the CEO and down that everything it does should prioritize the company first, and the person later. HR has been neglected, with recruiters consistently overhyping potential compensation. New policies are constantly put in place that undermine the employee (e.g. changing an employee perk so that it is as underutilized as possible).
#5 - Compensation & Hiring Process - Newer employers (2015+) are routinely under-compensated with potentially misleading guidance on the "upside" potential of a high valuation. Additionally, the hiring process takes too long (at times 3+ months ), and the recruiting team could be much more professional. Turnover rates are not low.