Disclaimer: I have used it three times, made requirements clear, and paid workers fairly, and had no problems.. but I am interested to hear about others' experiences.
they've introduced job success, now those who know how it works more or less or newbies with an empty job history -- are the top freelancers, whereas those who have been there for a long time, for years -- at the bottom. Needless to say, upwork doesn't disclose the exact formula used to calculate your job success.
more over: upwork claims it's guaranteed 100% you get your money if a job is hourly paid. No. they still can take your money and return it to a client.
they're many good freelancers who have been banned for no wise reason, among them are the top ones.
there're many other insights.
- they treat freelancers badly
- there're also a lof of other kinds of downsides about working there. google "why upwork sucks". or "odesk sucks".