Possibly the first big-world game.
Published by Activision
Designed and developed by David Crane
Platform: Atari 2600
Length: Short (Medium if played until mastery)
The Atari 800 version has a second quest!
This is the most advanced game on the old 2600. It's certainly so technically: it's got a large mapable, sometimes scrolling world with independently-functioning enemies, special regions, multiple modes of movement (running, jumping, swimming, ballooning). It's even got pretty good background music that changes based on the situation.
But its design is even more advanced than its programming tricks. While the original Pitfall's exploration-based gameplay was tightly limited by its three lives (for novice players) and 20-minute time limit (for advanced players), Pitfall II discards entirely lives, health, and even death. When the player touches a fatal enemy, the music changes for a bit and he's transported back to the last "cross" he touched, and he loses points depending on the distance. Crosses aren't too common, but they aren't too rare either.
The main thing this did for the game was remove the requirement of having to be really good to see it all. The original Pitfall had 255 screens and 32 treasures, of which probably less than 1% of owners had ever seen all of. Pitfall II, while still challenging, could be played continually until finished, with the player's remaining score still providing a substantial measure of skill that could be improved through further play.
The result is, interestingly, not dissimilar to Metroid without weapons or power-ups, but with a score. Pitfall II even has that game's search aspects: instead of looking for missiles and new abilities, players search for treasure. Not bad at all for a 2600 game!
Realizing that game-ending conditions other than winning could be discarded entirely was an amazing insight, and possibly marks the origins of the structure seen in 95% of games to this day: play until death, then send the player back to a checkpoint or previous save. While most of these games will boldly declare "Game Over" when the player runs out of health, considering you can always resume from the last checkpoint it's really not over at all. It's arguably an overused design now, but it wasn't back when Pitfall II did it.
Notice that Pitfall II leans even harder on score than Pitfall! did. While the origin of the concept of score goes back to pinball and earlier, is an oft-neglected aspect of gaming these days. Sure, there are "experience points" and "hit points" and "magic points" and a dozen other points, with more introduced every time a Japanese RPG tries out a goofy new system, but most games have shied away lately from providing measures of skill. Exploration games, in particular, tend to focus more on finishing the quest than building up a score, but Pitfall II shows that they are by no means incompatible.
Not the first open world game, by a long shot, but refined the concept and introduced the Metroid structure that rules action-adventure game design.
Published by Nintendo
Developed by Nintendo R&D 1
Designed by Gunpei Yokoi and Yoshio Sakamoto
Platform: Famicom Disk System, NES, Gamecube (Metroid Prime), GBA (Metroid Zero Mission), Wii (Virtual Console)
Take a look, the game is composed entirely of horizontal and vertical-scrolling areas. They almost always alternate, that is, horizontal areas always have vertical areas connected to them, and vice versa. There are only two types of places where this trend is bucked: powerup rooms always connect horizontal-to-horizontal, and the final boss room is also connected this way.
Also consider for a moment the Maru Mari, a.k.a. Morph Ball, one of the strangest powerups in gaming history. Mario growing large from eating a mushroom is an obvious nod to Alice in Wonderland, but where the hell did this come from? It has become one of the most identifiable aspects of the Metroid series, enough so that the Prime games had to include it. When game designers sit down with a notebook and start jotting down abilities for their kick-ass warriors to have, turning into a small ball on command is not what one expects to see written down. Even less does one expect to see it survive the editing that brainstorm sessions demand. That it did, and that it became one of the signature elements of the games, says much for the elemental power of creativity in game design.
Metroid was not the first open world game, and neither was it the first side-view platformer exploration game, nor was it the first game where players found things in the maze to allow them to reach new sections. But it was likely the first game to take these different elements and rigorously mold them into a game-ruling structure.
Tellingly, the game starts out by immediately forcing players into a wall imposed by its structure. The first room (I'll call a single horizontal-scroll or vertical scroll area a "room") contains a powerup item, the Morph Ball. The third room contains a low ceiling that cannot be passed without it. If the player tries to tackle Metroid like Mario, always going to the right, he'll hit the barrier immediately; the Morph Ball can only be obtained by going left from the start.
In effect, by putting such a barrier in the first two rooms of the game, the designers are telling the player:
1. You can explore in more than one direction.
2. There are cool things in this game that give you permanent new abilities.
3. You'll need them to progress.
4. If you find a place you can't get by, go back and look for new powerups.
Modern games tend to be chatty enough that, were the game made today, all this would probably have been printed on the screen at some point, if not voice-acted. But Metroid is silent. Outside the opening and ending, there are only six words visible in the entire game. (They come near the end....) At the beginning of the game the player's explored area is limited, so there's not a lot the player can do other than go back and find the Maru Mari. Later on the player is more likely to be without a needed power-up, but by putting such a block almost at the start the player comes to learn the rule of powerup progression for himself.
The atmosphere is the thing about Metroid that holds up the best today. I'm not the first to remark that Metroid's awesomeness comes, by large part, from the fact that the game doesn't seem designed. It's easy to look at the chaotic arrangement of tunnels, large unimportant sections, frequent dead-ends and random strangenesses (like the "fake" version of boss Kraid that lurks in one tunnel) as signs that the game was created by computer. It's actually intricately planned out, but exploring the planet makes it seem like the level designer was determined to erase any signs of human handiwork. This makes Metroid what one might call a Lovecraftian game. It is easy to believe it the work of inhuman logic, built by beings unknown to us.
It's dangerous to say definite things about whichever game did something first, but the following seems safe enough. Metroid gave us the first large-scale use of granting permanent player abilities as a means of game progression. It gave us major powerups (Long Beam, Hi-Jump Boots, Screw Attack, etc) as both rewards and an advancement system, while also including many minor powerups (Missiles and Energy Tanks) that serve as simple rewards. Yet they too are essential objects; Energy Tanks of course extend the player's maximum health, but large numbers of Missiles are eventually needed to destroy the Zebetite barriers in one of the last rooms of the game. If the player hasn't found enough missiles he's stuck, lending importance to what might otherwise be a trivial collection goal.
Metroid Cubed, a fan recreation using a voxel engine