A smah hit!
It's just perfect, completely perfect. I did find a small bug though but it makes the game funner, when you carefully go through a portal thats horizontal you'll stand on the outside of the output like if there was a short invisible plank there. thats the only bug I saw. Even without a level editor I thought this game was fun. Maybe you should take a chance to add things that the original portal never had, Like different turrets. Also I noticed the G-Man in the windows that was cool as he walks away yet he never comes out any of the doors. Great job on a good game.