I started playing Part 4 before I realized you had released v1.5. Before that, I replayed Part 3, and I did solve the laser puzzle this time.
This is my blind playthrough, which took me 1:20:17 to finish. To be merciful, I edited out repeated failures, and one very long stretch while I searched for 3 dots in the main room. The connection between the button at the bottom and the door at the top was a surprise to me. I could have made this even shorter, but I decided to leave in some of my more comical failures, and one little glitch that occured with the cube in the funnel. I'm somewhat confident I found the intended solutions, except that in the laser room I didn't use the laser cube in the box on the pillar.
The Ledge, Part 4 blind playthroughembedded
oOd6ldN-H1gEDIT: While replaying Part 4 (room 276) on version 1.5, I encountered a fatal glitch. In the same place that the cube got stuck at the end of the funnel in the video, I accidentally dropped it on top of the Aperture sign. I could see no way to dislodge the cube from there.
I've read your comments to me and others about climbing the funnel in Part 1. I can't do it with or without the cube. The method I'm using (which worked for zivi7) is no more difficult with the cube, so why not take it with you? I couldn't figure a way to get the cube up there after I was up there, anyway. I guess I'll feel pretty stupid when I see the intended solution.
Overall, the scope and strength of the puzzles in this make this a solid 5 contender. But the visual clutter and obstructed sight lines made finding things in this a real bear at times. The erector set theme is well done and consistent throughout, except for all the glass walls that you just can't see. For such an open map in most places, I actually felt cramped for maneuvering room most of the time. If it were just that I didn't like it (not the case), I wouldn't dock you a point for it, but I really feel it gets in the way a lot. However, any map that encourages me to pound away at it for three days to finish it earns a bonus point. 5/5 from me.