For example:
Stein’s avant-garde collection challenges the reader to think of ordinary, everyday objects and concepts in ways that they hadn’t before. This is in direct contrast to...
I was told that in this case, "this" should be followed by a noun, as it is an adjective. I know that "this" can be substantive, but is that just informally, or is it acceptable in formal writing?
You were misinformed. Almost all of what most contemporary students call “determiners” (a class distinct from “adjective”) may be employed as pronouns with propriety in any register, formal or casual: this, that, each, every, some, quantifiers like some, few, many, and their comparatives (more, less) and superlatives (most, fewest), ordinal numbers, and possessives. The only ones I can think of offhand which cannot be employed this way are the articles and every.
Indeed there is a burgeoning school of thought which holds that these words should be reclassified as pronouns.
