I'm going to be totally honest: I don't understand Steam's Big Picture mode. I don't know what they're trying to accomplish with it and it seems like they did a very small thing and then tried to make it sound like they changed PC gaming forever.
All they really did here was make the Steam interface easier to see on a television. Literally that's it. The fonts on Steam are pretty small, which is fine when you're sitting a foot from your computer but makes it slightly difficult to view on a television from your couch.
They also made it easier to control via gamepad, but I don't see that as much of anything at all. They didn't magically make PC games playable via gamepad and they didn't encourage developers to start making their PC games playable with one. Yes, there are a lot of PC games you can play from Steam that are gamepad enabled, but you certainly didn't need Steam's permission to frickin' plug one into your computer.
So all this amounts to is a slightly easier to use interface for a television. It doesn't change games or gaming, it just made Steam a little more convenient if you want to go through the trouble of connecting your gaming computer to your TV.
Full disclosure: we already have a computer connected to our TV. We use it to view Hulu and Netflix because both interfaces are better in the browser than they are via apps., not to mention Hulu's ridiculous failures with cementing contracts to actually stream most of their shows via apps. So, for me, and I'm sure many others, connecting a computer to my TV isn't anything revolutionary. Plus, the computer we have connected wouldn't even be able to run Steam.
Which brings me to my next issue: I think there is a significant difference here between being able to game on your couch, console gaming, and PC gaming. I PC game when I want the precision of an FPS and I am happy to do that with a headset, mic for Vent, keyboard and mouse...none of which I want to truck into my already cluttered living room. If I want to play a game from my couch, I'll play with my Xbox. Microsoft has crafted a whole experience for console gaming with the satisfying beeps of achievements, the feel of their specific gamepad, with games that are meant to be played from your couch at a distance.
Simply moving your computer into your living room does not replicate that experience. Console gaming is an entirely different feeling. Plus, I don't want to have to turn on my TV and sound system every time I want to check my email. Big Picture mode seems to imply that you are either going to have a spare gaming computer laying around, buy one specifically to put into the living room, or turn the living room into your PC gaming and/or main computing area. None of these options seem reasonable or comfortable to me. I'm not going to write this blog post on my television or tangle myself up in cords to constantly switch between computer screen and TV.
I guess it's just the way Valve presented this that seems so silly to me. They didn't do anything revolutionary...Steam is just slightly more convenient to use if you have the dying desire to use your TV as a computer monitor, or if you already have a spare computer that can run Steam connected. (Let's not even get into how system stressful Steam got after they added the Mac compatibility. I know a couple PC gamers that could go on forever.)
If you are excited about Big Picture mode or if you plan on using it, I'd be curious to know the reasons why. I realize that I am definitely not their target audience, so my perspective about this is a bit biased.
I also recognize that it might not be Big Picture mode itself, but the idea of using Steam in your living room that they are crafting, perhaps in preparations for the fabled Steam Box. However, if that were their reasons I would think this whole thing was even sillier since that would require a console type device and not an entire gaming PC, which also goes back to my feelings of console gaming via the Xbox vs. PC gaming and those intrinsically different experiences.
PS: First comment to try and turn this into a PC vs. Console penis size contest gets banned.