Well I'd define game as being a task with defined rules intended for enjoyment so osu! would be a game by my definition.
What do your friends define as being a game? Is Super Mario Bros just a sim for running and jumping in 2 dimensions and any FPS an armed combat simulator? Clearly with the Guitar Hero example the accuracy of simulation doesn't matter.
What do your friends define as being a game? Is Super Mario Bros just a sim for running and jumping in 2 dimensions and any FPS an armed combat simulator? Clearly with the Guitar Hero example the accuracy of simulation doesn't matter.