The best place to look for factors on what defines a publishable literature review might be in the publication guidelines for respected literary journals. Each journal will produce a set of guidelines to help authors of literary criticism articles in the submission process. Each journal has a set of standards that guide article length, titles for criticism, theoretical perspectives, etc.
Also, become familiar with the styles of literary criticism articles that are published in the field. University and college libraries have these in their online databases--Academic Search Complete or Premier provides many journals in literary criticism.
That said, factors that seem to be standard in published articles are a clear theoretical perspective, a critical position on a text that is nonstandard (i.e. its a given that The Great Gatsby is a story about illusion vs. reality so who would publish an article about this unless the writer has something special to say about it), and heavy engagement with and familiarity of the text.
The Explicator is one of my favorite literary journals; you might consider reading a few of the articles in the journal as an example.