A system's limitations spawns one of the best series of all time and the stealth genre itself.
The game begins with Solid Snake infiltrating Outer Heaven, a heavily armed nation in South Africa, in order to rescue fellow FOXHOUND member Gray Fox and ultimately destroy the nuclear-equipped Metal Gear. Snake is without equipment at the start, forcing you to sneak by guards and use your fists as weapons until you become better equipped. However, most guns can alert guards from the noise when firing. Once you gain the suppressor, which eliminates the sound a couple of guns make firing, your tactical options increase quite a bit. Various items and weapons familiar in the series make their first appearance here, including remote-controlled missiles, mines, rations, and the famous cardboard box.
There are a total of eight keycards in the game, which are used to open locked doors. These cards are either found in rooms or dropped by enemy bosses. The cards are the key to progression, as new areas are often found behind locked doors. However, you usually have a few options of where to go, like multiple floors on an elevator, and can get a certain distance on each floor before you meet an obstacle to your progression. As a result, you'll find yourself searching areas for the card, you may find it fast or you may take a lot of time sweeping over various rooms. While the cards function as physical keys, various items serve as virtual keys as well. A room full of poisonous gas isn't passable until you find the gas mask, an electrified floor is a barrier until you use a remote-controlled missile to destroy the control box on the far side, and so forth. In essence, you'll spend the bulk of the game searching for the next "key".
There's just under a dozen bosses in the game, with a wide range of special abilities. You'll encounter machines like a Hind, a tank, and the Metal Gear itself, and people equipped with various weapons. Sadly, about half of them can be killed easily without taking any damage due to positioning and wise weapon choice (the remote-controlled missiles are very powerful against certain bosses). The battle with the Metal Gear is rather interesting though due to the way you must go about destroying it.
In addition to the named prisoners that you must find, there are also a number of generic prisoners of war scattered throughout the complex. The more that you rescue, the higher your rank increases. Your rank determines how large your life bar is and how many items you can carry. Some prisoners give you some critical information when you rescue them; make sure you remember what they say as they won't be there to repeat things. This is especially true of the method of defeating the Metal Gear itself.
One negative about the game is the amount of backtracking that is required. Even if you know exactly where to go in the most streamlined way possible, you'll still have to go back to an area you've already been to get an item, then head back yet again to where you were. This is obviously necessary due to the technical limitations of the day, but once you figure out the "puzzle" of the movement patterns of the guards on each screen, waiting for them to get into the right position to make your move yet again can get a little tiring. There are a number of segments where you must travel over a dozen screens back, then the same dozen forward again. The fact that where you must go isn't always clear adds to this problem. Sometimes when you need an item to proceed (a gas mask for example), chances are it's in a room that you weren't able to open before but have since gained the key. But which room, in which area of the building? Since it's not clear, your only real option is to just run around and check random rooms, hoping to stumble upon the right one.
Another problem is the rations and ammo capacity. Due to the technical limitations, what you do on one screen isn't remembered when you head to the next. So, if there's a ration in a room, you can grab it, head out and back in again, and repeat this process until you reach your limit. If you make some big mistakes and burn through your rations (an issue at the beginning but not at the end when you can carry quite a bit), simply return to the nearest ration spawn point and restock to the limit. Shortly into the game, you should never have a problem with ammo or health. The extra rations may be welcome at times, though, due to the guard AI. While you need to punch guards to damage them, they damage you if they simply touch you. When you turn to face them, they tend to get out of the line of fire. If they're close enough, they run right through you to get behind you, and when you turn around they run right through you again. I found this rather annoying, though it's probably balanced when you consider how easy it can be to dodge their slow bullets.
The graphics and their level of detail are rather good for the era and system, capturing the situation about as well as could be expected. The environments can vary from deserts and building interiors to rooftops and watery areas. The sound is decent as well, it doesn't really stand out but isn't bad either.
The game itself takes about two hours to finish if you know exactly where to do, and about three or four hours if you have to search for your next objective. Once you experience the game, there probably isn't much reason to play it again at this point, especially seeing that just about every item is required for progression in some way or another.
For those not turned off by decades-old games, most Metal Gear fans may be interested in experiencing the roots of the series for themselves. With the MSX version of the game available as a bonus in Metal Gear Solid 3: Subsistence, now every fan can play the "official" version of Metal Gear themselves. However, those that love the Metal Gear Solid series primarily for its story will find Metal Gear's minimal story rather disappointing. Other than the plot twist at the end (which those whom have played a Metal Gear Solid title should already know), you spend just about all your time finding items and cards to move further into Outer Heaven towards the Metal Gear itself. Still, for those interested in the roots of the Metal Gear series and in video games in general, this game is probably worth a playthrough, especially due to it coming with Subsistence.