I have to say that this mod is actually very fun to play around.
The Portal gun mechanic leads to different ways to traverse some stages and get items and Stars.
But there are some issues: it's kind of bothersome to have to keep transitioning to the first person camera and having no indication of which Portal you're shooting; the game is very glitchy because it wasn't supposed to work this way, and sometimes you can fall through the ground to the depths of the underworld.
Overall, I'd recommend this one for someone who already played the original game and wants a somewhat new experience for a fun spin.

Pros: the Portal mechanic gives new possibilities
A very fun new take on the original experience

Cons: glitches. Lots of them.