More game play options and especially a level editor for arcade mode or endless ,with save points, would increase the appeal of the game .
The idea would be that different people could create different sections in arcade mode and choose a different difficulty cap and that is where their stage would be slotted in to an arcade game of dead nation . Given this model players would never know what would be next because of the range of creative input into the stages .Many options would be available .Specific task option ? BOSS or no BOSS play .Drop a weapon to pick another option ?
I think that games loose appeal when they become predictable .The addition of difficulty is not the magnetic factor for the player .It is the the same,same ,same and just more difficult .
Throw in user created stages and see how interesting the game can be ! The art work and model of Dead Nation is excellent except that it is restricted by it's own repetition . User created levels would add a dynamic to the game !
This is the problem in that the developers perceive that a game has a use by date and to some degree this is true . A game that becomes repetitive too quickly or has been played a few times quickly becomes second hand .So they strive to make something new for the sake of new ! Why not just improve what already has been invested in ? OK people have stopped playing .Why ? Get the players interested to play again and produce such a good update that gets them talking to their friends .With good strategic advertising as well !
If I were to be able to create a level for arcade and if it could be rated then Arcade would be much more a return too game .The choice of arcade games to play would never be the same .Some more option to Zombie behavior would be implemented .For example more Zombies could jump over greenery ,the money stage .