This is actually quite fun ! The puzzle system is simple and effective, it makes for nice puzzles and platforming.
Here's a few things that I think would improve the game :
- In the first level, shooting will kill you because you destroy the portal that's positioned properly. Maybe you want to deactivate the portal inputs until a few levels later when you explain it.
- Show which portal you currently have selected
- Deactivating the portals when it's invalid instead of killing the player would make things more clear.
Great job on the game, I enjoyed it !