I would like to know this to understand why some games like Mario is still playing today and because no other. This is to implement in future game projects.
What are the factors most important to developing a game?
Gameplay or Graphics? Both?
EDIT:
It's Possible combine these two?
The most important is that you ENTERTAIN your target users.
Some users want gameplay. Some users are wow-ed by just graphics.
This might be a bit old-school for most peoples liking, but I'd have to say gameplay.
Put it this way, I still find myself running old SNES games I loved on an emulator these days, but I can't see myself playing a game that had great graphics but rubbish gameplay after it has had its time.
Both are preferable, but it's gameplay that generates the classics of each era.
I would say it depends. For indie games, gameplay is the most important because that's what will keep your players entertained. obviously for big budget games, you need both to be successful. But as long as your graphics are clean and neat, players shouldn't complaint too much.
Gameplay, combined with the often-missed concept of ease of play. If I can't pick up a game and make progress in a couple minutes I probably won't go back to it after I've been away. It's just disheartening to have to relearn how to play a game. Mario tended to have simple interfaces, one or two commands only, which makes it easy to come back to. Comes back to this: http://xkcd.com/484/
Gameplay. So many modern games just seem to spend their entire budget on developing an incredible graphics engine and forget to include plot / interesting gameplay. One example is Doom 3. It's kind of interesting, and spooky to play, but it's SO REPETITIVE. Tunnel after dark, deserted tunnel... compare it to Doom 2 which had a plethora of different types of missions. Doom 2 had crap graphics, but there's a reason people keep playing it.
That being said, a big reason people play old games is from nostalgic value. The gameplay might not be particularly excellent, but it does bring back memories, so that automatically adds value to the game.
Graphics are, of course, also important... you can't get away with 16-color 2D sprites anymore (or at least, not as easily). Rather than spend the entire budget on graphics, though, look into an OK graphics engine, and spend some time making the game:
Distinguish between designing the game and programming the game. For a programmer, a game is simply an application, no different from any other kind of software. Game design is a whole 'nother beast of a different color :) If you can program well, you can program a game well.
Good game designers are the same kind of rare creative as good storytellers--who aren't necessarily always good writers.
The think the real importance is addictiveness, which, of course, is rather hard to program in. However, I think the key to that is a task which is very easy to "almost" achieve. It's the "I'm almost there; just one more try" effect that keep most people coming back.
Gameplay in terms of being easy to get the basics but difficult to master would be one factor, for sure. For example look at Diablo II for something with some nice basic elements but also some elements to keep playing for a long long time, like horadic cube recipes for example.
Replayability is another factor. How much does the game change if I pick a different starting character, assuming a game with this style like an action RPG or FPS or beat-em-up(Street Fighter II)? Is the game enjoyable from different views? How good is the AI if I have computer opponents in a real-time strategy game and how many settings are there?
Graphics can be a nice complement but just because a game looks nice doesn't mean I'll spend hundreds of hours on it. Titan Quest would be a nice example of taking the Diablo II style and adding some eye candy that makes for a nice game.
Nostalgia is a big factor in why some old games are still played like the old Super Mario games. The memories of playing those old games and seeing how cool it was to get to the next level can be why some will go back again and again. It is the reason why I still play my SNES at times.
Game play is what gets you hooked, especially if there's a very low learning curve such as pacman or breakout. Graphics is what sucks you into downloading / buying a game. Sometimes nice graphics is a demo don't necessarily translate to a nice game. I've seen so many games that have beautiful front screens, background, etc. but the actual game graphics such as characters, objects, etc. suck. Generally it's a good idea to think about your game design to make it easy to understand and play initially, then it gets harder with later levels by adding bosses, threats, bonuses, increasing speed, etc. Then fine tune how the game looks with snazzy graphics.