What I’ve found is that the simpler a game’s controls are, the more accessible it is to people, and the more people that get to enjoy your game. Purely in financial terms that means more money but from a karma perspective it means a little bit of extra joy in the world for more people and that’s a big win for me.
The sheer success of Angry Birds (and Cut the Rope) should give you an idea of what can happen when you take the simplest control scheme possible and wave it under the noses of 50 million people.
Only just beyond Angry Birds in terms of complexity we have non-reflexive point-and-click games which sometimes involve a tiny bit of drag and drop; these too are incredibly accessible and lend themselves to huge mass market penetration and enjoyment. In this group we’ve got games like Farmville and Scrabble and all those hidden object games.
Then we move on to realtime control which immediately excludes about half the playing population right there. Many people simply do not have the hand-eye coordination to play reflexively, nor even the inclination to try. Even so you’re still talking about a massive number of people who can potentially play your game and enjoy it. Plants vs Zombies is one of the simplest distillations of realtime point and click. At the other end of the spectrum you’ve got Revenge of the Titans and StarCraft, which though very complicated and probably very difficult games to actually master, are reasonably trivial to actually control in a basic fashion just using a mouse to point and click at buttons. All the extra buttons used - right mouse, scrollwheel, etc. - are all optional controls which are unnnecessary to actually play.
We can branch out explosively at this point into game control mechanisms which are basically “difficult” at this point, excluding huge swathes of potential target audience simply because they are, well, too hard for most people to master. I should remind the reader of my wandering post at this point that you are not most people. Twin-stick shooters and other controller-based schemes; WASD+Mouse-to-aim; pretty much any variation on those two control schemes augmented for 2D (Ultratron, Astro Tripper, Gravity Wars, Renegate Ops, Soldat), 2.5D (Doom), or full 3D (the entire FPS and TPS genre), with increasing complexity for each dimension further massively shrinking your potential market and the number of people who are going to enjoy the controls.
Then you get into just plain broken schemes like Arma II (I bought this specifically the other day to check out the Day Z mod but got on so badly with the irrelevantly complex control system that I stopped playing and never tried the mod). But the less said about that the better. Let’s just say that if there’s a genre your game appears to fit nicely into don’t break the accepted wisdom of how control should work - i.e. in an FPS it’s WASD to move, mouse to aim, LMB shoot, there’s an interact key, etc.
Cas 