Here you have the greatest video game of all time, Ocarina of Time. Along with it you have a question "What made the game so successful?". Then you have a game like Psychonauts or Beyond Good and Evil. These games were given high scores by the critics, the people who played them loved them, but they failed to succeed. There's probably a whole bunch of reasons why they didn't succeed, marketing, too high budget etc. But what I'm interested in focusing on is actually the gameplay itself, the immersive experience.

I'm sure there are other games to look at apart from these. But what are your thoughts on why a game like Zelda was so successful and others which were given great ratings weren't? What is it about Kingdom Hearts that makes it such a cool game? What did these games do right and wrong? etc etc etc

Also considering the following, Cavestory (great gameplay and great story, old graphics and old sound) what made this game so fun? It was like playing Super Metriod in a new, innovative and unique fashion. So it leads me to think that the main difference with adventure games is that the story has a larger part to play in how fun the game is??? If that's the case then assuming we have the story down, what could we create and do to make magnificent gameplay?

I'd really love to hear your thoughts so please share.

im not sure about any of the games other than zelda and super metroid, and i think what makes them so successful is the non linearity (not in the sense that you can do whatever you want) but there are loads of side quests... and they arent random quests, they all have something to do with the story, or have stories of there own.

It's because Zelda is famous. Who wouldn't get the newest of the very best, but get something else?

I am not an expert on these things but I think you may be confusing "Greatest game of all time" with "most popular game of all time". I think Zelda and Metroid are so popular because they have such simple story lines. Complex story lines are often distracting, whether it be movies books or games. Look at adventure games like Siberia and Dreamfall or even Myst. Great games if you like that sort of thing but to complex to the point of boring to the majority of gamers.
I think Zelda was so great because the story is straight forward and people can relate to it. And it had a variety of challenges.
Also I do not think you cannot emphasize enough that Zelda was designed for teenagers with gameplay that could be enjoyed by their younger siblings and that could also enjoyed as these teenagers grew up. Most kids games are discarded at a certain age. Zelda has incredible longevity. Another thing about games like Zelda is that they seem to be interesting only to people who played them as kids. Young adults do not seem interested in these games so I think the success of Zelda has a lot to do with successful age group marketing. Being available on a handheld was a big plus. Being acceptable to parents is also a huge plus. Game developers don't seem to notice that Nintendo has made a fortune with games that parents will buy. Zelda has certainly benefited from that.
I think that most adult games like Psychonauts should be considered niche games and they will never appeal to a mass market like Zelda.
Gameplay should be simple I think. I remember trying to play the Spiderman game and thinking that the swinging was like some kind of weird physics test. If gameplay is to complex then people get irritated. The point of a game is to be able to kill the monster with 10 hits from your sword. 5 hits... the game is to easy, 15 hits the game is to hard and I have better things to do!

One of the greatest parts in zelda for me was the fact that, when you got the bombs, you could finaly go back to that crack in the wall you found at the very beginning of the game to get an extra heart container...

... I did not play psychonauts though .

Has anyone played Cavestory? It's a free downloadable game, just google it.

It's a PC game, very very good gameplay, imo on par with Super Metriod. It's the sort of game which proves you don't need great art resources to make a great game, just your imagination, skills and time.

Sorry, I think you asked for specifics and I gave you game philosophy.
I have not played a Zelda game in a while but these are the aspects I think were great:
the collection of unique weapons that were relevant and useful. In many games the intermediate levels are just power ups that do not seem relevant to fighting the level boss. the gradual collection of weapons I think kept the player engaged. I especially like the hook shot and of course bombs are always good. The controls were usually very simple, you did not have to learn new controls for each weapon.
It seems that you are interested in making this type game so here are some thoughts on what might make this type of game better:
Increase the NPC AI. One of the great things about the Call of Duty series is the way the NPCs have improved. Now the enemies run away, hide,return, attack and the squads seem to provide real back up Increasing the AI in a any game would be a real improvement. Storyline branching. If the character choices have an impact on the story line then it would be a much more immersive experience.

Why zelda was more successful?
Commercials and console packs including the game.

EVERYBODY knows Zelda - next to nobody has ever heard of Psychonauts.

You can download a demo of Psychonauts at Steam! Its definitely worth a try!