What's the most important element of a great game?

Some buy games for their innovative designs, others purchase them for their atmosphere. What is the most important element of a great game...?

I picked fun, but from the economic view.
A great example for this is Resident Evil 4, it has the worst story and simplest gameplay I ever witnessed, yet it is so fun, that you like to play it over and over again(which doesn't apply to everyone ofc).

But for me personally, Atmosphere is the no.1. Games like Oblivion(with mods), Project Zero 2 or Silent Hill(part 2 or 3 only imo) have that special something delivered through the unique atmosphere they offer.

FUN,FUN,Fun...till daddy takes the T-Bird away!

For me its the game with the most innovative features. I've played way too many games and new features really draw my attention.

One of the biggest things I take into consideration before I buy a game is whether or not it has an editor.

Definitely not graphics, most modern game developers spend to much time developing overly realistic graphics and spend to little time creating content for the game. There is a reason why most modern Single Player games can be completed in a single day while older games can keep you entertained for weeks, or months.