This'll be a short one, but one of my favourite and what I personally believe to be an underrated book is "Dead Meat" by Patrick and Chris Williams.
I absolutely LOVE zombie, apocalyptic, dystopian, utopian gone wrong, type of novels. I've always loved how, besides the action and horror of survival which the characters you follow face, you get to see and experience humankind and how each person deals with it. You get to see group dynamics, how groups make decisions and what those decisions and their consequences are. I like to think about this sort of thing because I always wonder how I would react and what I would choose to do in those type of situations. If someone were infected due to a bite, would I agree to kill that person out of mercy or self preservation? If my group and safe house was over-run, would I sacrifice those who are left behind? If supplies were low, would I really consider stealing and possibly murdering another group for their supplies?
Apocalyptic books, especially ones with zombies, have always peaked my interest for this exact reason, and unfortunately this genre can become very cliche and cheesy very quickly due to the high amount of apocalyptic books and movies there are out there. Some do this genre a great justice (The Walking Dead, 28 Days Later, even Sean of the Dead was a great one) and some just...ehh, I dunno (Resident Evil as it got further in the series and strayed away from the simple outbreak and into this mutation genes that resulted in becoming this super natural being or something like that...I dunno, I lost interest). But I've always wanted to write a zombie apocalyptic novel :D Maybe one day, I can follow the ambitious example of Patrick and Chris Williams.
The thing for me that can easily put me off of a zombie apocalyptic novel is the characters. Characters are the pinnacle of the story. You can make up whatever excuse for how the infection began: Mad cow disease, a flu gene gone wild, a infectious disease that was contained in a lab but escaped, spores from plants...but if the characters aren't likeable, they aren't real, they don't sometimes make stupid decisions out of fear, sorrow, or just plan desperation from survival, and they don't react REALISTICALLY to what is happening to them...then they become these plain and boring characters. My biggest beef is that these characters are so fake, so 'overly confident' or 'somehow know how to start a fire with nothing but their breath and starlight' then half the time I'm just saying to myself in my head -