Making a game with a long term experience without having it lose its fun is really difficult to achieve.  For this reason there's been several mechanisms used in order to prolong a game's lifetime and still be enjoyable for the players.  In here I analyse two methods described in two different satirical games developed by Armor Games.

Upgrades

This is probably the most ancient of mechanisms used to extend the gameplay features of games.  It has been used to improve basic game mechanics such as in some action or adventure games (Megaman series, Prototype, Infamous), to add substance to the game experience such as in most RPG games (Fallout, Baldur's Gate, Mass Effect) and complement the game story such as in RPGs and Adventure (Fable) and the Sims games.

Upgrade Complete is a game that shows in an exagerated manner the way upgrades work in a game.  In a way this game is intended to criticise the abuse of upgrades to enhance the general game concept. 

However I've played this game and seen others played it as well; although some people may think that it explains very well the faults of an extensive upgrade system, most of Upgrade Complete's players have found themselves immersed in the game trying to reach the maximum upgrade to everything (and sometimes they have even tried to find more upgrades after the Game Over).

The most interesting thing about this game is that it is basically just a scroll down shooter in which you have the opportunity to upgrade everything.  This goes well with the modern trend of having everything customizable and upgradable to meet the player's expectations. 

Some may find that having the choice of upgrading the game menu is ridiculous and doesn't fit with a game's purpose, but isn't this customization of the most basic parts of an interface what has made web 2.0 succeed?  Isn't this kind of interactivity with everything what is making the users more confortable with their products?  Beyond the whole satire idea of Upgrade Complete, I think the concept points more to the future than to an actual mock up.

Achievements

The advent of Steam achievements, XBox Live Achievement Points and PlayStation Network Trophies have made this mechanic more popular every day.  And with a good reason it has succeed in extending game experience.  However, this is probably the most misunderstood since it has been used to emphasize game events rather than ask the player to strive for greater challenges.

Achievement Unlocked shows in a glimpse all the kinds of achievements that are most frequently used in games.   If played completely one will be able to distinguish the type of achievements one would like to find in a game from the ones that doesn't really matter.  

The first type of achievement you will find is the one that awards the player for just playing.  In Achievement Unlocked this is represented in the most silly way by giving an achievement for "finding the sponsor screen".  Although this may seem nonsense it is common to be found in some games. 

The perfect example I've found for this is Braid.  In this game (at least for the Steam version) the achievements are given everytime a level is finished or a jigsaw puzzle is solved.  It's true these events are true accomplishments but they don't add to the game experience, they are in fact necessary to end the game so they are achievements that will show sooner or later is you play the game completely.

Other type of achievement is the one where they award you for learning to play.  In Achievement Unlocked this is represented by achievements such as "Learn to move westward".  This one made me laugh a lot and I there are a lot of other ones like this in Achievement Unlocked.  But the most ironic part is that I've also seen achievements like this in serious games.  An example is Defense Grid: The Awakening where they give you achievements for such things like upgrading towers, building more than 5 of a type of tower or even selling towers.

The third type of achievement is the one where they award you for making a mistake.  This would be probably the most unwanted kind to find in a game since it completely contradicts the concept of the word "achievement".

And finally you will find the ones that are worth achieving.  This are not common achievements and could be better called Challenges.  They add to the game experience and gives the player something fun to do besides the regular course of action of the game. 

In Achievement Complete they are listed such as "Hit points 3-1-4 in that order" or "touch every touchable block".  However, for this example these achievements may be too simple or easy to accomplish but they surely represent a challenge to the general game experience.  You may find this type of achievements in games such as Team Fortress 2 and World of Goo.