It's quite good experience. I enjoyed remastered graphics, especially in scenes with chiaroscuro, soundtrack is also praise worthy. First tests were really easy, but they get bit harder later, and new gameplay mechanics refresh the gameplay. I found story to be mediocre, there was unused potential with Amelie character. Overall it's not perfect but still fun and it's impressive to get something of this scale for free.
I beat the first 3 chapters last night, and it was a lot of fun! They have to do updated versions of old training puzzles that were pretty easy, but the environment, level design and overall production value feel like an paid DLC, not just a fan-made map.
Definitely recommend for anyone who loved Portal 2.