It is a very subtle mix of elements that makes one appreciate a particular magazine. Some of these elements are exchangeable, or exclusive, but here is what comes to mind (randomly):

Size
Materiality (binding, stock, wrapping, etc.)
Pagination
Printing
Price
Title
Frequency of publishing
Content:
””editorial structure
””theme
””photography (quality, style, content, titling)
””writing (quality, style, content, titling)
””advertising (quantity, type of advertiser, aesthetic quality of)

and then, some more subtle relations between these aspects:

Writing vs photography proportion
Design
Consistency between issues
Ability to renew itself over time