NEO 2 So Many Spikes : this one may be the toughest of the rank. Do know that at least first and last lemming have an important role

NEO 4 Tower Of Sacrifice : created by IchoTolot so blame him for the difficulty ! Once you made one Lemming a climber, you must notice that the music is "I Will Survive". So please make him survive at any cost. Really nice level design by Icho where things fall into place by themselves afterwards.

NEO 5 The 6'' Escape Plan : one of them Lemming has to Escape this very poor level design. Via thE uppEr or downEr routE is your choicE.

EON 2 Trust Your Lucky Star ? You have intended for the talisman which saves the blocker : start bashing when the climber is about the height of the Lucky Star ! To my knowledge, this is now the only way to get through the vertical structure w/o using the blocker.

About intended solution using the blocker you are also right : just start bashing at any time, and stop the basher with a blocker when the climber is safe from the traps.

EON 2 Head Bang Bump Wash Dry Turn Blow This one is not that hard, the solution is in the title. Look at the Head of the worker which :
Bang : when he is a digger (you have to be a metal music fan to get the headbang concept )
Bump : when he bumps his head while building
Wash : when he bashes under the water
Dry  : when he walks under the shredder
Turn : when he is a blocker
Blow : When ... Oh No !

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%