Ive just started writing up (in third year, social sciences) and when i get the feedback of each draft of each chapter back from my supervisors (up to fifth chapter now out of 7), there's hardly anything there to go on and improve with. There's a few typos highlighted, and things like 'you could do with another ref here' but other than that, its really hard to know what else to do to improve...how much should i expect? I kinda want lots of red pen all over it, for some reason!

well maybe its a sign saying what you produced is good!

hmm maybe try asking your sup what they thought about your chapter, and if it needs improving ? or whether its good as it is? ask to maybe have a meeting about it?

I would expect my supervisors to comment on coherence and robustness of argument. Highlighting typo errors is just a cop-out and sign of lack of knowledge of your research area. Ask someone other than your supervisor(s) to comment on your work. I'm sure they will point out other issues.
Good luck and keep us posted

Thanks Hairui - that's what I'm a bit worried about. It does feel a bit like a cop-out, but i dont know if im expecting too much...I have asked if it's 'good enough', and my supervisors say stuff like 'i think so', and 'its getting there', but Im not sure how to make it 'there'...

Glad to be of help. An alternative would be to present your work at relevant conferences and see what the audience have to say. What about other academics in the university? Some post docs are really helpful with proofreading.