Game Franchise

I HAVE CHOOSEN  “Metal Slug” TO MY TOPIC!!!
Essay 1.  Students will be required to analyze one gaming franchise where for the purposes of this assignment, a franchise is defined as a gaming media property with at least three titles in the series; for example, Halo, Diablo, or Final Fantasy are all fine, but Titan Quest is not.  What makes a game in this franchise stand out relative to its competition?  What are the essential qualities that entries in the franchise share that competitors (which you should be able to identify) do not?  Is one game in the franchise particularly noteworthy compared to the others?  Note that I am not seeking an essay on why your favorite franchise is the best, but rather an insightful analysis of how the franchise carves out a unique identity for itself.  Essay 2 should be between 1200 and 1700 words.
Example ideas:  What makes the multiplayer of the Unreal Tournament different from the same in Halo?  How does a Mega Man platformer play differently from other NES experience?