I didn't want to click on other threads in case of spoilers . I've got among my to-read pile, but I haven't read TKAM for nearly 15 years. I can't really remember much about it, so bearing in mind I am a very slow reader, should I just read the synopsis or actually reread it?
I think it's better read as a separate book and not as a sequel as the characters are quite different. I think it was written first, then rejected. So it's not really a sequel if that makes sense, although it is set later in the time with the same main characters.
I wish I'd read TKAM before GSAW came out - I'd previously read it as a teenager and not touched it again. I saw TKAM in a different light, reading it as an older person. However, what I don't know is if I'd've noticed these things without having seen the reviews of GSAW - I think it coloured my perception. So, if you haven't seen any reviews of GSAW, and you haven't read TKAM in many years, I'd reread it and see what your take on it is before getting into GSAW.