Kind of a mixed bag for me. On the one hand it suffers from what every fan-made portal puzzles suffer: they're either too primitive or too overcomplicated. As a result, the game varies between being too simple and being extremely tedious and clunky. The plot is also messy, it relies too much on repeating the Portal 2 formula, but the pacing is completely off, you spend too long in the first act and rush through the other two, and the ending is... yeah. And in terms of originality, though it may be not too honest to ask a fan made mod to reinvent the game but after Portal Reloaded the experience feels lacking.
On the other hand, the voice acting is really fun and well done, I enjoyed the part of the game with Emilia specifically. I also really enjoyed the locations, especially the surface world. It looks really refreshing for a Portal game. Music also fits the game very well and I could easily mistake it for the original Portal soundtracks. And at the end of a day it's still a game with portals and it's hard to ruin that.

Good puzzles, great story, cool achievements.

From my steam review prior to 100%ing:
The environments and characters of this game were incredible. The new puzzle mechanics were interesting and novel, and the overall puzzle design was great. There was a few non-puzzle areas I dislike simply because of their use of extremely out of the way portal surfaces for progression, which is admittedly consistent with base Portal 2. I really wished I could continue to follow these characters, though there was only three of them, they all were really interesting and in my opinion still have more to show. The finale was incredible. Well worth 6 hours, can't believe that this is free.

I am so torn.

This is a 4.5 star mod with visuals that consistently rival and at times exceed the base game, new puzzle elements that feel like natural extensions, and level design with an astounding amount of care put into it - there is not one straight corridor or empty room.

However, as a Portal sequel, it is brought down by the fanfiction-esque writing and voice acting, and puzzles that don't iterate and put enough spins on each mechanic. It feels like we are scratching the surface of each addition, but I wish I had more "aha" moments.

Granted, I am the worst possible audience for this - a long-time Portal player who autopiloted through 90% of chambers. I can imagine the structure and pacing working better for someone new to the series.