9 The Acid Test : first roadblock to me. There are so many was to free the right crowd that I did not know what to do at first. Finally I gathered both crowd together to make things easier for the builders. Timing on thoser builders was the hardest part, but it allows to save much needed time.

11 The Boardwalk : solution differs from Kaywhyn's. No containment needed, just some well placed diggers.

13 Cream Of the Crop : probably a important backroute. 5 destructive skills left and 9 Lemmings in more than requirement. Also the right part of the level is not used at all. Look at this poor Lem I sent over there, only to let it fall to its death when I realized he was not needed.
I'd say one is not supposed to be able to get throught the One Way pillar with 2 bombers only.

18 Kessel Mineshaft : I particularly loved this one ! Compression is easy to achieve with the many blockers given. Mining the big wall at the end is satisfying, though I may have it done not the intended way because I'm left with some miners.

20 Deux Ex Lemina : Great level for which one trick is used : the trap is actually inactive ! Is that on purpose ? In any case it helped me use the single builder elsewhere, and not the overcome the gap at the end. I save one more than required. Completely different solution than kaywhyn's

21 High Rise Lemmings : this one made me smile too. Solution is quite visible from the beginning, but I did not understand the use of the rightmost exit at first sight. Only when the blockers were freed that I thanked Scotty for putting it here 

23 Separation Anxiety : very good one ! Clean separation achieved thanks to the 3 blockers provided. Just count correctly how you split the Lemmings between the 2 groupes, or you wont save enough.

25 Down To The Wire : headache inducing level. I struggled a lot to find a correct order to dig down those wires, and to manage timing so that the gap can be covered properly. Good level for sure!
Also another example of Scotty's touch : inactive trap ! Though this one has not use in this solution anyway.

27 Open Season : hardest of the pack for me. I finally released and blocked all entrances with a single basher, all the while liberating a single worker to do the first part of the job (this release was possible with a single pixel of terrain missing, luck !?)
But then later you have to release another one for building over the bear trap. At this time I had a very dense crowd from which it took me a while to figure out how to extract a single worker again. But finally a well placed miner did the trick.
I think this level is very open ended, and ingenious. Great work !

30 Upside Down World II : nightmarish web, glad I could finally get through it. Spider responsible for it can go burn in hell.

Sour 5 / Sweet 2 (major design change, Sour 5 solution change)
Sweet 2 is still very accessible due to the 50% save required. But it prepares well for Sour 5.

Sour 5 was another story, quite hard now ! I used the "turn a miner with a blocker" trick to save miners needed on the right part of the level. Though the hardest part at the end was to turn that miner so that the crowd does not splat. By some kind of miracle and after many tries, I did it and unwillingly made a precise settings which uses "you fall between diagonal connecting pixels". With this setting, not only the crowd does not splat, but they all fall down in the good direction ! So I even saved a blocker here. Not sure this is intended ?

Sour 6 (design tweaks, solution overhaul). Now I find the level actually easier than before, but this may be because i did not find intended last time and struggled a lot with the timer. I think it is perfectly fine now.
The hardest part for me was to figure out how to save some time at the end : if you set the last delaying basher not high enough, the crowd will make a long way before turning back and you run out of time ! Setting it properly leaves plenty time and I could even save 100%

The clever solution you give makes very little use of the crowd : just need a bomber apart from pionneer. Intended uses the crowd a bit more.
I always think interaction with the crowd is better ; if the pionneer can go in by himself, then the whole "Save One" theme falls apart.
I'll certainly work a bit more on the vertical structure to enforce things. I have to find a way to ensure that if one lemming bashes through the structure, then he cannot stop without using a skill.