Re: the idioms, the one phrasing in one of the office logs that had struck me as particularly awkward was the line “They’re holding way too overkill of equipment for simple security so what are they here for? They seem particularly needed in the higher floors...”.
This sentence, as phrased, gets its meaning across and might even go unremarked upon as an off-the-cuff comment in a stream or a conversation at a bar, but it's actually extremely weird, uncommon and grammatically incorrect. The most egregious bit is ‘overkill’ being used as an adjective (‘way too overkill’ in the same way you might say ‘way too angry’). The word ‘overkill’ is actually an uncountable noun — you would never say “way too overkill”, and this speaks to my overall feelings about the way the dead characters articulate themselves in these logs; it's all very nondescript phrasing that an average civilian would use in a casual context, and not a clean-cut professional in upper management.
Like were it me expressing this sentiment (and mind you, I'm a military veteran but this would apply even if I were a normal office wageslave), I'd probably write the above sentence as something like “These guys are far too heavily-equipped to be normal security guards, so what are they even doing here? It seems they're being stationed in greater numbers on the upper levels...”. It's clearer, more specific. But that's just me.
I forgot to add, one thing I really liked about CotD is the UI design. The font choice really helps to make the action feel like it's being played on an old VHS tape and that really enhances the zombie movie feel of the VN.
Thanks again!