Corporate Plunderer (aka Snidely) set a challenge before me last night. He is interested in developing a game for mobile devices that would satisfy a list of conditions:
Can be played concurrently but does not have to be
Variable number of players
Obviously everybody is trying to be highly addictive, so that isn't anything new. Variable number of players isn't too big a challenge for a game on a computer, that is more of an issue that physical games have to deal with. The main problems as I see it are that allowing people to play a game without having specific time constraints is extremely difficult unless you want to make success and failure not really possible.
For example, there are many online games where you can build your farm, set up a city, or rule a small empire within a larger game world. In most of these games failure is not an option - you can log in whenever and if you don't log in for awhile it is ok, you are exactly where you left off. In those sorts of games if failure *is* an option then the game is often extremely random since you can be easily smashed by others who team up and strategy is relatively useless compared to luck and politics.
This sort of situation is much easier to deal with if you have time constraints - if a single turn goes by each calendar day for example, everyone can realistically log on and give orders for a few minutes each day. It is also possible to arrange a game where you log on and are paired against an opponent immediately as is the case in many online games, but the market for directly confrontational games is often limited and you are faced with direct competition from real FPS and RTS games on consoles and real computers. There is also the issue of having fairly serious intensity and dedication required for 1v1 matchups that a mobile platform is not especially well suited to - people often have only a little bit of time to play and may be interrupted.
I think it might be a good idea to consider a team PVE approach to this sort of problem and a great starting model would be WOW's random dungeon finder. What you would need for this to work is some kind of persistent 'character' that can advance over time through winning games and a social platform where people can hit a button to group up with their friends or random others to play a game together. It would also be possible to make the advantage from each game decay rapidly such that each game played after the first on a given day awarded half as many points as the game before so a casual player won't fall too far behind a hardcore player.
That is a fine bit of structure I think, the trick of course is designing a game that a few people can play together on small screens with limited controls and easily scalable difficulty. That, of course, is no small task.