The largest barrier to entry in games is control. People sometimes take for granted the years of experience they may have behind a controller, keyboard or mouse and an interface convention breaker like Wii really helps get more people on board. If input is proven as a huge limiting factor for hitting an audience then you have to be as careful as possible that your input choices map to the audience range you are targeting.
My input system has started being largely based on the input in a game like Starscape (great indie game you should check out either on steam or their site). This hasn’t been an active decision, just the quickest method for me to get the ship flying around and shooting rocks. But now that my game is off the ground what input methods “should” I consider and how would this affect the game and its future growth ability? I see three options: keyboard controls, mouse+keyboard and predominantly mouse with hot keys.
If I go with the method I currently have, I believe that I am targeting people that are fairly technically inclined with the keyboard and are used to driving a character with at least 5 buttons. I would have the left/right movment, acceleration and deceleration as well as some kind of firing button. The games that I would be similar to that I enjoy are Star Control II (one of the best games of all time and you can get an open source version here), Starscape, Crusader and many more. I find that this method is somewhat easy to learn but I wouldn’t consider it a casual friendly interface and I would say that it tends to fit in the action/skill category where people need to learn how to fly each potential ship that the game would have. The melee mode in Star Control II would be the sort of target for my design if I went in this direction. The controls would allow for me to make unique flight characteristics and weapons firing modes as the core of the experience. One thing to note is that if I was mixing any other game experience in like an adventure or navigation component, I would most likely still be using the mouse.
Option two is the combination of both. The most interesting combinations of this for me in the indie gaming community are Crimsonland and Alien Shooter. Both of these games require the movement from the keyboard and shooting with the mouse. Abuse was probably the first game I recall playing like this and it was a great ambidextrous combination of killing might. For me this method of dealing death has some sort of arcadey rewarding feeling and it maps to a gamepad fairly well. So even though there may be more going on, it can feel more intuitive when learned and offers greater control over shooting direction with minimal additional “buttons” to learn. This combination of controls would make me push my game in the firing upgrades as the primary growth avenue and movement as the secondary. I would want more enemies to target.
Finally there is the most casual approach of all. If you stick to the ethos of mouse control (preferably with it being possible to use just one button) then you get into the realm of games like Diablo or even RTS like control. The advantage here is that you clearly have a design rule that you can do everything with the mouse and it makes sure that almost anyone that uses a computer should be able to at least play your game. You can also layer in more hotkeys or movement controls if you want to ala Scavenger (another great indie game) or even like Diablo. If I went this route, there would be less arcade action and it would be more about target selection and upgrades to your ship/character.
Thinking of input decisions is making me start to think of my target audience and the experience I want to create. The funny thing for me is that in my game history the games that have stuck with me the longest offer multiple mechanics, but typically keep the interface to them the same (Star Control II, X-Com, Starscape and many more). Currently I am leaning towards trying to implement a mouse only version only because it would be the most accessible and “pure” design but I think it would take the game away from action. I will let you know what I decide and that might be by trying them all!