While there is a lot of detail in the game, and there is realism to body damage you inflict, in combat options, in stamina and knockbacks, and in weapon degradation (the upgrades are clever too). The rest of the game is rather not as polished, and not intended to be realistic, and more fun instead. The plot is actually left a mystery in the first game mostly, while your focus is on surviving and leaving, while the plot is actually well-fleshed out (No pun intended) in the second game. The sequel also balanced combat and tightened up controls a little bit.
Its not realistic by a long shot (hard to say for sure since I was never in such a zombie infected situation), but if you like the development of the series so far, the next spiritual sequel is being worked on by them called Dying Light.