A standout title of the 2D resurgence.
Cave Story is a game that existed for quite some time as a freeware game before it was released as a WiiWare title with updated graphics and audio. The fact that it made the jump from a free PC game to a $12 Wii game may sound like anyone paying for it is getting ripped off, but this is such a quality product that not paying for it is absurd, and was only ever an option because it was made by a single guy with no means of publishing. Cave Story is a well done game in most every respect, and offers a good blend of old school side scrolling action and new, interesting features.
The way Cave Story plays is pretty straightforward, you run, jump, and shoot your way through many varying environments that make up the larger world, and find upgrades to your health, weaponry, and mobility in a manner not unlike Metroid or Castlevania games. It's not surprising that Cave Story is referred to as a "Metroidvania" style game, but I do feel like there are some things that set it slightly outside that title. For one, the world is not quite as large, maze-like, and as full of power-ups. Most of Cave Story felt fairly linear to me, with small side paths occurring just often enough to keep me looking for them, but I did not have to spend hours backtracking across the world to find most of the secrets. For me, this works in the game's favor, because it keeps everything focused and forward moving.
Probably the most interesting mechanic in Cave Story is the way you "level up" your weapons. Every enemy you kill drops experience, which, when gathered, adds to the total experience of your currently equipped gun. Enough experience nets your gun a level up, which usually results in a pretty dramatic increase in it's power. The catch is that your guns level quickly, but taking damage from anything causes your equipped weapon to lose experience, and will often cause your weapon to level down. This puts a whole lot more focus on combat, especially on avoiding enemy attacks, than any Metroid or Castlevania game I've played, and makes every encounter important and terrifying. Cave Story is definitely a difficult game, and can occasionally be frustrating, but there is no doubt that the difficultly adds that special something that really makes it a memorable experience.
There are a lot of other things about Cave Story that make it interesting - secret weapons, multiple endings, the dark, magical nature of the world, and a giant talking toaster. Overall, there isn't anything serious to complain about unless you just don't like the old school style that Cave Story brings to the table.