Feedback is always very helpful, especially such extensive one, so thanks a lot! 
15 RIVER
Producing chaos - sounds deadly
20 MOROS' CAMPAIGN
The size and finding out what to do, makes this imo one of the hardest levels in the set. There is however no order in which you have to solve most puzzles; as soon as one is accessible you can choose to do it, or save it till the rest is done, and in the end you need all, as you need all three objectives to get to the exit. So it's not that mean in this regard. Each single puzzle is not supposed to be that hard, but some are not trivial, like the flamethrower one. If you end up, with a parity which isn't resolved that easily, an approach would be, step on some aoe buttons randomly, and try solving it again, since the probability to run into one isn't that high.
25 OH NO! MORE PUSHING
The difficulty from the first to the second sokoban ramps up really fast, just as in the lemmings game the title is referring to. I was a bit worried, that I made it a bit too tricky, so good to hear that you solved and enjoyed it.
26 100 SWITCHES
It's supposed to be a mathematical puzzle, in other words, no guesswork is required. Since I'm not a hundred percent sure, what makes the hints unclear, I'll try to explain them here first:
Part 1 reads: EITHER USE EVERY SWITCH ONCE THEN EVERY SECOND ONE, THEN EVERY THIRD ETC.
Part 2: OR THINK ABOUT IT AND SAVE YOURSELF A LOT OF WORK.
I guess it's the first phrase in part 1, use every switch once (a comma is missing), where use might not be unambiguous - which means step on a switch, so if it was off before, it will be on afterwards, if it was on, it will be off. A better verbalization might be, step on each switch one time.
Then every second one, might sound like there are two ways to interpret it in the first moment, but as long as you keep in mind, that the game has to terminate at some point, you know that 1, 3, 5,... is not an option.
Executing all the steps from part one is a lot of tedious work, that's where part two kicks in, which means, which switches will be on, and which off, after the termination.
The main question is, would the wording for part one Either step on each switch one time, then every second one, then every third etc. make it perspicuous, or are there more problems regarding the hints?
15 RIVER
Producing chaos - sounds deadly
20 MOROS' CAMPAIGN
The size and finding out what to do, makes this imo one of the hardest levels in the set. There is however no order in which you have to solve most puzzles; as soon as one is accessible you can choose to do it, or save it till the rest is done, and in the end you need all, as you need all three objectives to get to the exit. So it's not that mean in this regard. Each single puzzle is not supposed to be that hard, but some are not trivial, like the flamethrower one. If you end up, with a parity which isn't resolved that easily, an approach would be, step on some aoe buttons randomly, and try solving it again, since the probability to run into one isn't that high.
25 OH NO! MORE PUSHING
The difficulty from the first to the second sokoban ramps up really fast, just as in the lemmings game the title is referring to. I was a bit worried, that I made it a bit too tricky, so good to hear that you solved and enjoyed it.
26 100 SWITCHES
It's supposed to be a mathematical puzzle, in other words, no guesswork is required. Since I'm not a hundred percent sure, what makes the hints unclear, I'll try to explain them here first:
Part 1 reads: EITHER USE EVERY SWITCH ONCE THEN EVERY SECOND ONE, THEN EVERY THIRD ETC.
Part 2: OR THINK ABOUT IT AND SAVE YOURSELF A LOT OF WORK.
I guess it's the first phrase in part 1, use every switch once (a comma is missing), where use might not be unambiguous - which means step on a switch, so if it was off before, it will be on afterwards, if it was on, it will be off. A better verbalization might be, step on each switch one time.
Then every second one, might sound like there are two ways to interpret it in the first moment, but as long as you keep in mind, that the game has to terminate at some point, you know that 1, 3, 5,... is not an option.
Executing all the steps from part one is a lot of tedious work, that's where part two kicks in, which means, which switches will be on, and which off, after the termination.