So, what in the world is Last Day?
Last Day is a mod pack, and is to Call of Misery what Call of Misery is to Call of Chernobyl; it adds content on top of the original, but differs considerably to an extent of which it cannot quite be classified as an addon. It includes not only STCoM and some other usual stuff, but also several addons previously unknown to the majority of the western S.T.A.L.K.E.R. community, such as MLR, which adds a lot of new characters and tasks, or an extended edition of Outfit Addon, adding not only outfits and helmets already present in the regular version of Outfit Addon, but also several variants of all types of apparel - regular, worn and damaged.
There are many more such changes, it is a very large overhaul.