I finally finished the puzzle level I was working on. It's got two block-pushing puzzles, one based on lighting fuses in the right order, and one based on falling blocks. Personally, I think the difficulty is an uneven mix, but I'd appreciate feedback. The level in question is called UPB Babel.
I also finished my timed level, UPB Endurance. Once you light the fuse, it takes just under two minutes for it to reach the target, during which an infinite army of bots will pour out of a line of unreachable spawners. There are two health powerups that get uncovered as the fuse burns down and some obstacles to provide some cover. It may even be possible to hide under something for the duration, but since this is basically a score attack only that would just be silly.
Finally, I reuploaded my Sadist level after making the changes that occurred to me while I was posting it the first time (swapping the upper and lower rooms). It's now a bit harder, since you can no longer avoid fighting the fastbots. See the original post about it for the new level.