I guess since I was able to milk another joke out of Nintendo's Nintendogs, I'm obligated to talk about it.

On the surface, it may seem kind of dull to constantly care for a bunch of cyber-dogs, animals that need food and water every time one turns on the game, and that stuff costs money. To earn money in the game, you have to take your dog to competitions (Disc Throwing, Agility and Obedience) and earn the prizes given out for finishing in the top 3. Coincidently, this also earns Trainer Points for you, which gets us to the real heart of Nintendogs - Unlockable Content.

The more you play, and the more points you earn, the more features are made available to you through the wonderful concept of unlockable content. Pokemon probably wins the crown for unlockable content by encouraging players to find hundreds of little critters and "catch 'em all." Nintendogs is a little more modest, having only 20 canines to find, and 6 of those are available to the buyer of the game - the exact six dependant on the version (there are three different versions of Nintendogs) you buy. The rest of the animals are unlocked either by earning Trainer Points or by trading with your friends.

There was considerable excitement at my house over the weekend, because one of my dogs had given me the elusive fireman's hat, which allowed me to finally pick up the dalmation puppies at the kennel. The dalmation and jack russel are two dogs that are not initially available to players of any version of Nintendogs and must be unlocked through diligent playing.

That's an example of Unlockable Content where it works. In both Nintendogs and Pokemon, the unlockable characters are part of the game itself and you can use them as soon as you unlock them. Where it doesn't work is where the content has little or nothing to do with the game itself, such as unlocking photos from the wrap party when that particular game was finished. It's hard to come up with really useful unlockable content, because it takes a lot of work to come up with something so useful in the game and once you've done so, it's hard to resist the urge to make that available to the player to ensure that the game has enough content to begin with. Games like Pokemon and Nintendogs had long development cycles where they could carefully balance what they wanted to give to the player and made sure it was available at just the right time in the game.

Food for thought.