The idea is to create a game entirely from scratch, in C (with a little bit of C++), entirely on stream. He streams for about 2 hours every night at 8PM PST and will be recording the creation of the entire game, while providing commentary on everything he's doing and why he's doing it.
I've watched a few episodes so far and it's been really great. It's a great watch if you have some scripting experience and want to learn what it takes to make a game outside RPG Maker (or even if you already know C/C++ - I've already learned a few things watching him that I had no idea about). He does a really good job explaining nearly every single line of code, and archives all of his videos on Youtube, if you want to reference them later.
If you've never done any C programming before, he also did a short "Intro to C" series of videos as a setup for the game-development videos. It's not necessarily enough if you've done no programming at all before, but if you have a little scripting experience, you should be able to keep up with most of what he's doing.
Anyone who's interested in more game-development-related stuff should give it a watch, I highly recommend it.
Casey's Twitch stream: http://www.twitch.tv/handmade_hero
Youtube archive: https://www.youtube.com/channel/UCaTznQhurW5AaiYPbhEA-KA
As far as what kind of game he's making, well:
Spoiler
(Someone on twitch chat): "Since you said you aren't a game designer, how do you plan on designing a good game like this?"
"...I understand the basic mechanics of game design. I can do a traditional game just fine. Like, I'm sure I can handle a game that isn't avant-garde. So I'm not going to make a game that is like, 'oh, it's the emotional journey of someone as told through the eyes of their pet goldfish who got cancer recently and had to go to a... thing, but it's really a dream sequence and at the end you realize something about, you know, your sexuality or something."
"...I understand the basic mechanics of game design. I can do a traditional game just fine. Like, I'm sure I can handle a game that isn't avant-garde. So I'm not going to make a game that is like, 'oh, it's the emotional journey of someone as told through the eyes of their pet goldfish who got cancer recently and had to go to a... thing, but it's really a dream sequence and at the end you realize something about, you know, your sexuality or something."