As a semi newcomer to the series (I never played any of the games until I got SR1 cheap for PC, and almost didn't get SR2, except because of a whim) I love these games. They are story writing at it's best. Defiance is no let down on this fact.
Although, I wouldn't say Defiance is replayable due to events in the game like others that are a new game every time. But if you are a fan of truly well written stories, then Defiance will impress you every time. Drama, sacrifice, betrayal, discovery, it has it all. The graphics ar eimpressive. The music will astound you (or bring back memories for old fans because they are remixed versions of the previous games music). Crystal Dynamics has made an impressive game with each new addition. This is definitely a game worth buying.