If you follows games news and release cycles, you'll probably be aware that single player games having a multiplayer component is the vogue right now. Most people aren't very happy with this - the announcement of Bioshock 2's multiplayer seemed to annoy people in particular - but its purpose is to "extend play time" and "add value", so say the back of the boxes. People also seem to mention "replayability" a lot when talking about single player games, promoting it as "adding value" as well.

The problem is that games studios, and in fact players, assume these are ways of adding value inherently. That is to say they follow the 'more is better' approach to consuming content. In my eyes, this a wrong assumption.

Competitive Multiplayer Components: Diverting resources away from the main mode of a game is rarely a good thing. It means there are fewer developers are working on the single player, and have less to work with, so it only makes sense that the single player will be of lower quality then it could be. That's not to say that a conventional multiplayer component can never enhance a single player experience; being able to engage in combat/contest with an enemy far more dynamic then game AI can allow you explore the game world in new ways and have different emotional experiences. However few studios have as good resources as Bungie or Infinity Ward, so multiplayer modes rarely end up being worth playing at all. Not that they're bad per se, but why would you want to play Uncharted 2's multiplayer when you could be playing a game that's been built from the ground up to be multiplayer, such as Team Fortress 2? The result is that additional multiplayer game modes are often a waste of resources.

So far I've been referring to conventional implementation of multiplayer, i.e. deathmatch, capture the flag, and all the other usual game modes. It's worth thinking about unconventional multiplayer as well though. Take Brink for example; allowing real players to take the place of bots to try to thwart a player or group of players as they progress through a storyline is a really good way to enhance the single player experience. Demon's Souls' message leaving system is another way multiplayer interaction can enhance a single player experience. So we can conclude that it is possible for multiplayer to enhance single player, it just requires that the right kind of multiplayer is implemented, a kind of multiplayer that works with the single player.

Co-Operative Multiplayer Components: Co-Op can enhance the single player experience greatly; exploring and area or working together with a companion to take down a boss can convey narrative and generate experiences that really increase your enjoyment of the story. However this doesn't mean that by adding co-op to a game you are automatically adding to the value of its single player. I feel Half-Life 2, for example, is a kind of game where co-op would and confuse and detract from the messages and experience that the game is trying to convey, because it would completely mess up the relationships you have to the NPC characters, and destroy the pivotal illusion that you are Gordon Freeman. As it happens, co-op has actually been developed for the game in the form of the Synergy mod, which I've played and haven't really enjoyed at all. So as with competitive multiplayer, whether co-op really adds any value to single player really depends on what kind of game the single player is.

Replayability and Bonus Content: Yes, I know its not really a word, but everyone else uses it so I will too! Replayability is quite complicated when it comes to adding value. To use two earlier examples; I've played HL2 the game through many times and have easily got more 'value' out of it then I payed for, and Demons Souls is a game specifically designed to be fun when replayed. However I think that to say that replayability inherently adds to a game's value, or that being able to spend time in a game without advancing the story (i.e. Assassin's Creed's flag collection) adds anything to the game at all, is a wrong assumption. I say this because some games honestly seem to lose value by having multiple playthroughs encouraged. This can be seen with Lucas Art's Lucidity, which I really enjoyed and played through in a single sitting. The artwork was beautiful and atmospheric, the gameplay engaging, and the story/message/context interesting and emotionally effecting. I didn't need collect-a-thons, bonus levels, achievements, or leaderboards in order to have the reaction I did, and yet the developers chose to include them anyway.

This bugged me as I felt that the achievements and leaderboards distracted me and took my attention away from from what the game was trying to tell me. It was the same with the firefly collecting; the fact there was an option to collect as much as I could and a reward for doing so meant that I felt compelled to so, which again distracted me away from the actual game itself. So, as with competitive and co-operative multiplayer, it really comes down to integrating replayability and bonus content into games that would benefit from it, and not into games that wouldn't.

As you can see, the prevailing conclusion I have come to is that when games developers and publishers look into adding value to their games, they should think more about what type they are making, and how it could be enhanced, rather then looking at which ways of adding value are successful. After all, whatever is right for everyone else might not be right for you!

Addendum: Oh and yes, you could argue that added value is only added to make games more appealing to customers and so make more money, meaning it doesn't matter whether it enhances the game or not, as long as it sells. To this I would use the age old capitalist logic response; "money is made by games that sell, and games that sell are games that are bought by us the consumer, so in fact we the consumer have the power to decide what makes money and what doesn't". Now if only we could use this power responsibly, rather then just buying X million copies of Uncharted 2 and scoring it on its multiplayer mode and replay value.