After completing this Mod a couple of days back, I can safely say that Only Puzzles 3 may be the weakest of the first 3, but it's not to say it didn't had its moments.

My main problem is there were a ton of contraptions that would no longer work if they were activated, then deactivated, so I would softlock my puzzles, it happened to me on the third puzzle room of the Moon Base, but these contraptions don't even need my input for them to stop working, I managed to get the piece in the middle of the 4th puzzle room of that same world since the jammed wall requiring lasers didn't activate, I don't even know why that is.

Then there's stuff that made no sense to me, like in the fountain area of World 2, you need to put specifically Cubes on the buttons for the contraption to work, but I managed to use extra connectors instead, but that wouldn't work, and when I realized that, I saw there was a respawning Cube on one side, and if I brought it to the buttons in front of the other sides, that would activate the other buttons in question, but leave the Cube the chance to respawn if I were to Reset the world, so there's an exploit. Furthermore, since I brought extra pieces, I even managed to go over the wall of World 2, and I didn't knew I was going into World 4 actually, but then I realized I may've softlocked myself there since I went in without unlocking certain doors, so I had to restore backups.

I also got stuck in one of the Tower's elevators, because I think what happened is I had the game save when I was still in it, but then I made the elevator go up, then when I closed my game and went back, the elevator knew it was on an upper floor, but I was loaded back to where I saved or something. Here's what it looks like, at the beginning of my (unlisted) video; https://youtu.be/gaTN7iKYE14

But as I've said, I did had fun still, for instance most of the puzzles in World 4 were very good, perhaps the same can be said for World 3, and there must be some more I've forgotten in the 2 years I haven't played it. I'm still looking forward to 4 since that one's been seemingly completed.