Cave Story has the player incarnating a tiny robot who can't remember who he is or what he is doing there, exploring the inside of an island floating in the skies, meeting its inhabitants, the Mimiga, as he goes. As it turns out, a group of scientists from the surface of the earth are there, as well, to study the Mimiga and the island. However, one of them, referred to as “The Doctor” seeks to use a special red flower found on the island to use on the Mimiga. The flower has the power to make the Mimigas who eat them go berserk and turn into monstrous giants with frightening destructive power. So the little robot who befriends the Mimiga people will try to help stop The Doctor's evil plans, finding out more about its own identity in the process.
The action is strictly a 2D affair. Despite the 3D graphics, which were in 2D in all previous versions, the scene is viewed from the side and still involves a lot of platform hopping, just like in a Mario game. The emphasis on exploration is quite strong, not unlike the classic episodes in the Metroid series, though the areas you will explore are far more linear with fewer branching paths.
The island is inhabited by many non-playable characters that the player can converse with either simply for progressing through the game and advancing the story, or just to find out additional background information on your environments, the story behind the island and its inhabitants, or even your own identity. The script is written quite well and leaves a feeling of mystery in the air at all times, making the adventure all the more interesting and the story that much captivating. Originally written in Japanese, the PC and homebrew versions had been made available in English thanks to fan translation. However, the English script used here is the same as the WiiWare and DSiWare versions, in which some items and locations are named differently.
As progress is made, the little robot will collect all sorts of interesting items, like keys to open doors, a map system, a jet-pack with limited autonomy, or even some of the NPCs' own lost possessions, which you'll want to bring back to them to get them to provide help in return. These kinds of fetch quests add a pleasant RPGish feel to the game which makes for a thoroughly rewarding experience. This is reinforced by the fact that the health bar can be increased by collecting Life Capsules, not unlike obtaining heart pieces and heart containers in the Legend of Zelda series.
Another important part of your adventure will be fighting enemies, and this is made by collecting weapons. Each weapon shoots in a different way. The initial weapon, the Polar Star, acts as a simple handgun; the Fireball shoots fireballs which hop along the ground a couple of times before extinguishing themselves; the Machine Gun, if shot downward, will make you hover in the air, making platforming sequences that much easier, etc... All weapons have infinite ammunition, except for the Missile Launcher.
The interesting catch with the weapons in Cave Story is their experience system. As enemies are destroyed, they may leave behind some hearts that replenish your health, missiles to replenish that supply of ammunition, or most importantly, Energy Crystals. These act as experience points which are added to the weapon you are currently holding as you pick them up. Most weapons, with only one exception, will increase in power as more levels are gained. Each weapon requires a set number of Energy Crystals to increase in level. The minimum power is level 1, and is maxed out at level 3. However, being hit by enemies makes you lose not only health, but also experience to the weapon you're currently wielding, meaning that avoiding being hit and constantly collecting Energy Crystals to keep that weapon's experience level as high as possible are primordial. This is the most defining aspect of the gameplay in Cave Story, and the most recognizable.
Collecting new weapons when you encounter them isn't compulsory, though. In fact, you may very well skip some of them and find out that this modifies the story to make some other weapons available which couldn't have ever been collected had you picked up another one before. This ensures that every playthrough of Cave Story may be approached differently.
Not only that but other choices you make along the way may also influence how the story unfolds a bit, opening up the possibility for multiple endings. This will have you try out the game multiple times to try and see what differences you can make happen, although discovering where those choices can be made may prove difficult without resorting to using a walkthrough or asking for help.
The major difference in this 3DS version is obviously found in the graphics. Although the WiiWare version, along with Cave Story Plus on Steam (for Mac and PC), offered the possibility to play with higher resolution tile-based 2D graphics, the overhaul here is far more significant. Everything is now made in polygonal 3D, although the overall level design sticks as closely as possible to the original, meaning that everything that once was accessible in the game still is. These new graphics add a wealth of fresh new details which make the whole thing all the more credible. However, the downside to this is that the higher level of details means that some platforms which could originally easily be made out among the rest of the scenery blend more with rest of the surroundings now, making them harder to distinguish in some occasions. Fans of the original won't have too much problem with this if they remember which platforms to hop on to reach certain areas, but this might make some of the hardest platforming sequences even harder to apprehend for newcomers.
Of course, being a 3DS game, a stereoscopic 3D effect was added, as well. Although it doesn't do anything to improve the gameplay, it makes the whole scenery far livelier. However, you might want to restrain from putting the 3D effect to its maximum.
In certain occasions, some elements in the foreground added to this 3D version will stick out of the screen too much, and this may induce a slight sense of sickness. This didn't occur to your servitor here with the effect halfway up, though.
The soundtrack has been completely remastered, unlike the “updated” soundtrack found in the WiiWare version and Cave Story Plus (although it seems that the remastered soundtrack was made available in the latter, as well, through an update). Some of the original tracks are definitely better rearranged than others, but newcomers won't notice and will still find the music to be damn good. The original music is, however, not included.
The Curly mode (which lets you play as Curly Brace) found in the WiiWare and Cave Story Plus versions wasn’t included either, nor was the Wind Fortress of Cave Story Plus or the classic version of the game with 2D graphics. The classic mode included only replaces the 3D models of the characters and enemies, along with some elements of the scenery, with their original sprites, while the rest of the game remains in polygonal 3D. This doesn't make for the best blend of graphic styles, though.
Apparently, according to NIS America producer Jack Niida, the 512MB cartridge was already chocked full of content as it is and couldn't hold the additional five or so additional megabytes that the original game weighs. It seems more likely, though, from a commercial perspective, that they didn't want to hamper the possible further sales of the DSiWare version available on the eShop and thus already playable on 3DS.
Nevertheless, this new version still comes with its few exclusive additions. A new area, the Inner Wall, was included, containing an item which is a nod to another game by Nippon Ichi Software. A few of the areas already there originally also have some whole new sections for themselves. Lastly, this new version holds more Life Capsules than any other version of the game, increasing considerably the maximum amount of HP that the player may collect in the entire game.