Once upon a time, I was playing card games like Valkyrie Crusade and Elves Realm for nearly 2 years while being completely unaware of Sid Story. Oh, and what I can tell you is that getting decent cards on VC or Elves Realm is a real pain in the heiny.
Fast foward, nearly two months into playing Sid, I was able to amass Sr and R+ cards which would have been utterly impossible if it was on VC. Other than that, the app design, screen transitions and elements of the game is really something unique which I come to love other than the cards. Not to mention, even the game mechanics is easily understandable. Plus, let's not forget even limited game currency can be easily obtained by free players which is not something most game devs would do.
Basically, I'm genuinely impressed in a whole new level with the developers because there have been lots of effort put into the game. Which is why I don't see myself quitting this game anytime soon or in the near future.