I have been on UpWork for roughly 4 months now and overall I'm happy with it. It's a very healthy marketplace that makes it very easy to quickly find a job. I never needed to buy any credits because I got contacted pretty much on a daily basis by companies looking for my skills, so that was very encouraging.
There are, however, a few flaws that I'm hoping UpWork will work on to improve the experience for freelancers:
1) The types of jobs tend to be on the less strategic side and fairly straightforward. I have a lot of corporate experience that could come to good use, but I can't find jobs at that level.
2) I know that UpWork has an enterprise tier, but it's unclear how as a freelancer I can access those jobs.
3) UpWork has several badges for freelancers to recognise their skills. However, it's not clear how those badges are assigned. UpWork keeps the rules about that deliberately secret, to avoid freelancers hacking them. Whilst I do understand where they are coming from, it is a bit frustrating for freelancers who work well, have consistently high reviews and have been on the platform for long enough, to not get any badge at all and not be able to understand why that is the case.
4) What I really, really don't like about UpWork is their desktop timer. First of all, I had to contact customer support twice in the space of a month because of serious bugs. Given that a freelancer's revenue depends on that app, it should work 100% flawlessly. Second, it takes six screenshots an hour and sends them to the client as proof of your work. You can stop the screenshots from going out (you might have done some internet banking and don't really want your client to see your bank statements, for example). But if you prevent screenshots from going out, it detracts some working time from the desktop timer. What's worse, they recently also introduced some tracker that counts keyboard strokes and mouse movements and again adjusts the timer accordingly. That's really not, for a number of reasons: a) it's highly intrusive and against GDPR regulation in Europe; b) UpWork never asked me for permission, nor does it make it clear on its website that it tracks this way; c) linking revenue and quality of work to the number of keystrokes or mouse touches is plain silly and goes way too far.
5) UpWork's customer service team is very friendly and quick in responding. They genuinely care about freelancers, or at least that's my impression. However, the engineering team took around a month to fix the desktop timer. Again, freelancers' revenues depend on that timer, so to take a month to fix it is seriously burdening on freelancers, who then have to explain the issues to their clients.
So, overall it's a good platform to find jobs, but I do have some issues with it which I hope will get fixed soon.