It isn't for everyone, and that's perfectly fine
I've been playing PC games since the late '80s. Ever since I was old enough to grasp a keyboard I was introduced to PC games by way of my uncle, who was in IT at the time and had access to basically every new piece of technology on the market.
As such, I acclimated myself to mouse and keyboard controls fairly early in my developmental stages, and it's a habit I generally stick to when playing PC games to this day. But not everyone is the same way, and Valve is looking to ease those people into PC gaming with the Steam Controller.
For that, they deserve a fair amount of praise, and a fair chance to prove their point.
When I shared the story regarding Valve's attempts to make Dota 2 playable with a Steam Controller, the discussion exploded. Some of the more popular comments noted that "Dota 2 would never be playable with a controller," and that "controller players would be laughed out of games." Let me say right off the bat as someone who has been playing MOBAs since 2005, I don't think the Steam Controller is going to fully replace the mouse and keyboard -- but it has potential.
Valve's goal is not to take over the mouse and keyboard setup by force for every single game. Alternatively, when they do launch the Steam Controller, developer support for 360 or PS3 gamepads isn't going to be magically shut off. The vast majority (if not all) of Steam's games are still going to support traditional control schemes -- that's not the problem. The problem is that both the mouse and keyboard setup and a traditional controller don't really work for some genres when you're playing on the couch.
For genres like MOBAs, RTS, simulations, some MMOs, and even a few shooters that reach beyond a controller's limits, it's really tough to play them on a couch without having a M/KB awkwardly placed over your lap and on a table. One portion of Steam's new strategy going into 2014 is to make PC gaming more accessible with a variety of Steam Machine options.
More and more I'm seeing new PC gamers getting into the scene by way of a living-room setup, hooked directly up to their TV using Big Picture Mode. Sometimes, they don't even have a mouse and keyboard attached, instead springing for a remote control or simply using the a laptop's touchpad to scroll to Steam. The Steam Controller furthers that vision by allowing another option for people like that.
Also, it's important to think of the possibilities of advanced controller mapping built into Steam's API. Typically, if a developer doesn't support controllers by way of plug and play, gamers are forced to look elsewhere for a "mapping" program, to "trick" the game into thinking a controller is a mouse and keyboard. I can't count the amount of times I've seen comments like "I don't want to boot up Joy2Key just to play this one game." Given the advanced tech on the Steam Controller, this solution isn't necessarily guaranteed, but it's more possible than the current gamepad limitations.
Looking back throughout gaming history, controllers had to come from somewhere. There was a day and age when keyboards were commonplace, then joysticks, then a basic one button controller, all the way up to the devices we know and love today. But in order for the medium to advance, someone has to shake things up -- and I think Valve is doing just that with dual disc-like trackpads and a customizable layout.
Valve isn't trying to replace the wheel -- they're just adding another axle. Although I don't plan on using the Steam Controller for every single game I own, I am excited to try it out on a few games that wouldn't otherwise be possible on a gamepad without the technology Valve has developed. It's an exciting time for games, and like all things, we should wait until the tech actually drops before fully judging it. Who knows? You might like it!