In order to maintain a person’s Flow experience, the activity needs to reach a balance between the challenges of the activity and the abilities of the participant. If the challenge is higher than the ability, the activity becomes overwhelming and generates anxiety. If the challenge is lower than the ability, it provokes boredom.
That is so true. The tricky part is that your audience will have a broad array of different levels of skill and intrest.
If your game can cover a very wide range of intrests it will be more successful.
eg: Battlefield 1942 was one of the first games that had all the elements of a fps, flight sim, boatsim, car driving,... and therefore became very popular and started a whole new genre there. (Soon unreal tournament went the same direction, as did other games,...) But there is an underlying stream here that made it popular, and that would be the flow described in the article. It was accessible for unskilled players, you could just run around and shoot anything, but skilled players also found their fun, and started performing stunts, standing on flying airplanes, diving under bridges, etc,... Add the massive multiplayer aspect to that, and you have a winner.
It should also be noted that when you make a game with a massive multiplayer environment, unskilled players may be intimidated by skilled players, and may get irritated by that, and just 'give up'. That's why you see some of the mmorpg games out there have a 'newbie' area.