The other power-ups in Metroid perform similarly. Only at the end of Super Metroid (SNES) is the player able to fully navigate the gameworld—without, say, the “space jump,” certain areas can't be visited. Also, the weapons, such as the freezing ray, change the way players deal with enemies. Often enough, the player needs to freeze an enemy and use the frozen nemesis as a jumping or grappling platform, rather than just destroying them.

This is my point—in the one game, you already have all of your navigation abilities at the beginning; once you learn how to use them to navigate the game world, you're set. From then on, it's shoot to kill. In Metroid, your character is like an infant in the real world; it takes hours and hours to gradually gain the abilities to fully navigate the world.

Games like Metroid and Turrican (and pretty much all games, actually) work on an "aporia and epiphany" model, to use terminology from Espen Aarseth. An aporia is some "thing" in the game that serves as a stumbling block to progress. For instance, there are plenty of areas in both games that are inaccessible by standard maneuvers. Another example of an aporia might be a particularly difficult boss or monster that consistently defeats the player. When players reach aporias, they either give up (I consider consulting a Website or hint manual to be giving up) or keep trying different strategies until they find the answer. The joyous feeling that comes over a player – who usually quite suddenly and almost randomly discovers a solution to a difficult aporia – is called the "epiphany." It's that, "Oh, so that's it!" moment when the issue is resolved and the game makes sense again.

Now, to again return to the theme. In Turrican, these aporias are almost always related to the sheer number or power of the enemies. True, there are some locations that require other tactics, but most of the time it's more a matter of how fast a player hits the fire button. In Metroid, an aporia might require a very precise maneuver only made possible with a combination of "power-ups;" a player may have to use the grappling hook to swing up on top of a frozen monster, and then use the spring ball to access a small tunnel. Of course, the only way the player may have noticed the tunnel was to use the x-ray power-up, which allowed him or her to see it in the first place.

The idea here is one of increasing orders of complexity. Turrican follows a constant progression. As the game progresses, the monsters get bigger (and there are more of them). Metroid follows an exponential progression. With each power-up, the game gains another order of complexity. In a way, getting power-ups actually makes the game more difficult, because now there is a whole new set of tactics to take into consideration.

Compare Metroid to a game like chess. Someone may argue that chess is more like Turrican, because all of the pieces already have their full powers at the beginning of the game. However, I see it as more like Metroid, since the tactics must change with every move. If a player has a queen in the middle of the board, he or she sees and plays the game differently than if the queen is still locked behind a row of pawns. The Queen piece, much like Samus Aran (Metroid's avatar), potentially always has awesome game-world navigating abilities. However, the key is "unlocking" that potential by getting her into the right place at the right time.

While the "power-up" difference between Metroid and Turrican may seem a trivial thing at first, I hope that this discussion has helped game makers, game theorists, critics, and casual players alike recognize just how profound the difference is. My hopes are that more games like Metroid are forthcoming, for while Turrican is certainly an excellent game in its own right (I lost literally weeks of my childhood to it!), it lacked an essential quality that would have made it even better.