So, this is a Portal 2 fangame. It doesn't matter what they called it: it's a Portal 2 fangame. That's fine, tho, it's a neat Portal 2 fangame, but it makes its inspiration very very clear.
The "999999..." joke (twice!), the solid light bridges, the laser cubes, the setting being an abandoned testing facility where an automatized male voice guides you over the brightest era of the building, but after the halfway points it starts falling apart because lack of maintenance on an important piece of machinery.
It's okay, and fun enough to play, but when you're playing you can't ignore that feeling of "I played this game, but better, before".
The time rewind mechanic is cool, but it's also more limited than Portal's... portals, and it shows: the last third of the game becomes slow and repetitive, as there's only so much variation you can do with "figure out what route those cubes need to follow so you can rewind later". A shame, because the first half it's very fun to play.
I have also found some slight glitches, although nothing too gamebreaking: a door opened without unlocking it first without buttons, and the physics engine reaaaaally doesn't like water, as cubes go usually flying around when you try to pick them up from a river.
For all it lacks on gameplay, tho, it gives on writing. The dialogue is hilarious and both Aria and Astra are wonderful and easily likable characters. The background storytelling you can get by reading emails forms an interesting enough story and rewards a bit of exploration, even if the computers aren't usually really that far away from the path.
All in all, what all its flaws, I enjoyed it. It's not perfect, but a fun puzzle game is a rarity nowadays and, if Valve keeps on not giving me more Portal, this'll do.