Mel brings a new protagonist with a new companion sphere, boasting over 300 new voiced lines, an hour of original music, and 22 levels that its creators say may take anywhere from four to twelve hours to complete depending on how well you think with portals. It looks quite pretty. And it's entirely free (if you own Portal 2, natch), available direct through Steam.
The mod plops itself between the first and second Portal games, though it starts before either of them. Another person is awaking from an experimental slumber, see. Here's the skinny:
"In the early years of Aperture: Science Innovators, Cave Johnson’s scientists rushed to get everything working to catch up with the growth of the company. Not everything worked as it should have. Mel unfortunately took part in a faulty test called the Aperture: Science Innovators Short-Term Relaxation Vault, falling asleep for years. Now, with a fake Cave Johnson telling her she needs to escape the facility and a new device called the Aperture Science Handheld Portal Device, her mind races with questions. 'Who is this imposter Cave Johnson?' 'What happened to the facility and its staff?'
"'What happened to me?'"
Portal Stories: Mel garnered went through Steam Greenlight while it was still being made, so its initial release comes directly through Steam, where it'll appear as a separate entry in your library without any fussy unzipping or anything.
I do like the look of its tacky '70s portal gun. Beyond that, well, I'll need to play it more to say. Hurry up, download!