Gaming wouldn't be the same, but it wouldn't be different.
If anyone else here is old enough to remember, the actual FIRST game of it's type was Atari 2600's "Adventure".
http://en.wikipedia.org/wiki/Adventure_(Atari_2600).
It's by far, in my opinion, a little more difficult than some Zelda games I've played. I still have my original and it works about... 1/10 times I try to play it.... xD Although, you're simply a square running around, find a sword to defeat enemies, it was basically the pre-Zelda Zelda game.
To my knowledge, this was the actual first, top-down, exploring, puzzle solving (although the puzzles were really simple, ie fight your way to the east end to grab the key, fight your way to the west end to unlock the door, etc.), side quests, easter eggs, a variable inventory in which secondary items are stored, selected and used, "dungeon bosses", etc. that has evolved so much to what we now know and love. The simple fact is, though, that the basic formula for Zelda was already there.
If Nintendo hadn't created Zelda, it would be a different gaming world, if for nothing but the lack of Zelda, but it most likely wouldn't be really changed. Adventure was in the top 10 selling videogames of it's time and it wouldn't have been long before someone else expanded on the idea and profited. I'm just glad Nintendo did so we have the epic (and officially best) video game franchise Zelda today.
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