From the Telltale Blog:

It's time! The third episode of Back to the Future: The Game, Citizen Brown, is here for PC and Mac! Now is your opportunity to find out more about First Citizen Brown, the mysterious leader of the bizarre version of 1986 Hill Valley Marty McFly has literally landed in.

Marty's not alone in this twisted variant of Hill Valley though as he meets his girlfriend Jennifer Parker, voiced by Back to the Future actress Claudia Wells - though she's not the Jennifer he knew back in his "good old 1986".

Unfortunately, it doesn't seem to actually be downloadable through Steam just yet. On my client, it's actually removed Episode 3 from the library and there doesn't appear to be anyway to download it yet, and the comments on the blog look like it's not an isolated issue. Hopefully it gets fixed soon, been looking forward to this since the teaser at the end of Get Tannen!

Heads up! It's on Steam now!
 
I'm installing it now. It's my density.

Yep, just saw it myself. Well, I know how I'll be spending the next hour or two.

I'd be all over this if I had the time. :/

 i thought this was for Half Life 2 Episode three, don't get my hopes up like that.

"  i thought this was for Half Life 2 Episode three, don't get my hopes up like that. "

" Heads up! It's on Steam now!  I'm installing it now. It's my density. "

"  i thought this was for Half Life 2 Episode three, don't get my hopes up like that. "

Sooooo any word on Episode 4 yet?

Oh, God damn it. I realize I should know better, but before I looked to see what board this was on, I got super excited for a fraction of a second.

" Sooooo any word on Episode 4 yet? "