I think this work's very heavy (4)
I believe the answer is:
tome
'this work's very heavy' is the definition.
'tome' can be an answer for 'work's' (tome is a kind of work). I am not sure about the rest of the definition.
'i think' is the wordplay.
I cannot quite understand how this works, but
'i' could be 'me' and 'me' is found within the answer.
The remaining letters 'to' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for tome that I've seen before include "dictionary?" , "Large scholarly volume" , "Hefty volume" , "Heavy volume" , "Large and scholarly book" .)