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

It would have to be the look, feel and atmosphere for me. I want a game to suck me in to a fantasy world, where it creates the illusion of another world. When this happens, the real world is forgotten.

Fun! I mean why do we play games? To have fun... Grant you atmosphere and innovation are more often than not huge factors in creating that fun. Especially innovation with the industry the way it is these days. Everything is the same... The gaming industry feels so monotonous these days, where as back in the 90's it was well... much more innovative and overall fun!

One big reason I love Saint's Row 2 so much, which is probably one of my favorite games since the turn of the century is because the game is just mindless fun! Yes it's insane, crude, vulgar, etc.. etc.. but it's insanely fun! The designers seemed to go for flat out fun with that game! AHHH feeling an urge to play it AGAIN!

I really hope they don't break the formula in Saint's Row 3. From what little info that is available the developers want to make it darker. If it turns into GTA4 I'm going to furious. If they slash out the customization I'm going to go postal at THQ headquarters. o_O

Mind you Silent Hill 2 is the best game since 2000 hands down, actually it's one of the best games evar! Why because it's fun to be disturbed by a game!

Honorable mentions

Vampire the Masquerade Bloodlines: Insanely awesome and underrated game, very immersive and very true to The World of Darkness cosmology. Being a huge VtM dork as a teen even doing LARP I followed the game, and they really got the feel I think White Wolf was always going for with that franchise.

Fallout 3: I know I haven't really talked about it much, but I did really, really love this game. It was just so short though... Grant you there have been a lot of mods, and DLC released for it since I last played it in early January I should give it a try again. But even as a vanilla game I really found this game FUN and immersive! Much moreso than vanilla Oblivion.

Now I'm tempted to mention Oblivion, but no... As much as I LOVE OBLIVION if it weren't for the mods I wouldn't love it. Oblivion unlike Fallout 3 can hardly stand on it's own merit. The vanilla game I found to be kind of boring actually.

Primarily for me its replayability, cooperative features and the capability to edit/mod a game.

I voted for The look, feel and atmosphere, but its really a combination of them all that keeps me playing a game.
A game can be innovative but if the camera angle and controls arent right for example, then i wont complete the game and it will probably be traded in.
If the game isnt fun then why play it?