Lot of low-level clients. Too many freelancers that you compete with but if you have the skills and good presentation, you can go a long way and earn good. Sky is the limit.
Problem areas - the site is not freelancer-friendly. Accounts get banned for very small reasons. Favors the client too much who often force freelancer to work outside the platform, blackmail for the ratings, refuse to accept work citing the quality issue.. sad thing is that all the disputes almost always go in favor of the client. If a client flags you even once, Upwork might ban you. It is so darn strict there so basically, you always work under a cloud of threat. That's the poorest work culture you are a part of.
No security in terms of your profile. Clients often take you for a ride.