I'm intending to write an IKCG review myself, and think I'm heading for a good 4/5 rating. The background and flavour parts of the book are the best, but where it falls down IMO are on a few issues such as some clunky and unbalanced rules kicking around in there, a shame considering what a tight ship Warmachine is rules-wise, and a smattering of other things that I feel would prevent me putting up a 5/5.
On the other hand, the background and setting information stuff in the IKCG is so good that without even seeing the IKWG I can feel sure that, if it builds well on what's been presented so far, I'll be giving that a 5/5.