The Locked Room Mysteries - A good start! The bomber route is of course the easiest to execute.

Unfriendly Neighbours - Nicely done trapping those zombies!

These lemmings and those lemmings - Another good solution!

Crowd Control - A very impressive solution that saves 39 and doesn't involve changing the RR! Nice one!

Thick and Thin - This level is very focused on multitasking - making sure each lemming keeps out of trouble. That didn't seem to cause too much trouble for you, though! Nice 100% solution!

A Sorting Problem - Now this is a very fun solution! Lots of moving parts to get the different skill types to where they need to be. Interestingly enough, there's an often overlooked game mechanic that actually makes this level much easier to solve. I might make a separate post about it!

The Big Dig - Another great solution!

Equivalent Exchange - I'm surprised how many unique approaches there are to this level! Great solution!

Fun with Lasers - I'm glad you enjoyed this builderless level! Levels without construction skills really offer themselves to interesting ideas and solutions!

Escape from Zombie Island - Wow! A 100% solution! You even managed to save all the zombies too! Incredible work!

Epsilon:

Unconventional Techniques - Thank you for your kind comments! I also often become very discouraged when presented with a difficult pack. I usually spend endless amounts of time on the first levels of a rank and get nowhere!
What Lems beneath - The trick with the falling bomber eventually led to the last level in this rank - What have we learned so far.
A different kind of problem - I agree that the general consensus that the third hatch is too fiddly and precise. I've put in a fix for this though!
Do I have to do everything? - Another great solution
Send only the finest Lemmings - A very nice solution. I like your variant here with the three blockers instead of four.
Precision engineered Lemming - Now this solution is very creative! Great work on this one!
Round the bend - I like your crowd control and timing here. Great stuff!
Don't forget the builders... - Great solution!
Tarry not! - Another great solution! I chuckled when I saw the youtube comments for this video. I had no idea you were playing through this pack just as I was updating it!
What have we learned so far - As previously mentioned, this level was intended to be a culmination of tricks from previous levels in the rank. In particular, the trick used in Unconventional Techniques and Precision engineered Lemming, where a lemming builds one way, and another lemming falls from the hatch and builds in the opposite direction. The falling bomber trick was also inspired by What Lems Beneath.

Delta:

Entrapment - Nice solution!
Panic room - Another great solution! I'm surprised this level has so many solution variants.
Any suggestions? - I don't consider your solution to be a backroute here! I asked for suggestions, and you gave one that worked
A Humdrum Conundrum - Nicely done!
Oh, those talented Lemmings - Another great solution!
12 Steps to Success - Perfect solution! I find it interesting that the stacker is the one skill that seems to give people the most difficulty.
The Incredible Squashing Machine - Very nice solution!
Make the most of your Lemmings - Another level with variant solutions! I especially like the way you make the glider dig down through the spike.
DEAR LITTLE BEASTIES - Great solution! This level is an homage to POOR WEE CREATURES from the original lemmings. A level that gave me considerable difficulties in my youth
Curse of the Lemmings - Another great solution!

Alpha:

The Locked Room Mysteries - Nicely done on 100%!
Unfriendly Neighbours - A great solution! The main problem behind this level is that the zombies can't be gotten rid of, unless you get them up in that top right room, of course...
These Lemmings and those Lemmings - The direct approach is fine here! Bombing through the one-way walls is perfectly valid, the only issue is that you have to save every remaining lemming!
Crowd Control - Great solution! I'll lower the lemming count, so it's not so tedious to wait for them all.
Thick and thin - Nicely done! Saving 100% on this level is tricky to do.
A Sorting problem - Very nice. But I've made a change which should really ramp up the difficulty!
The Big Dig - This is indeed a backroute. Once again, the direct approach works well
Equivalent Exchange - Very nice solution! I find that laserers are very interesting skills. There's lots of potential for interesting things here.
Fun with Lasers - Another great solution!
Escape from Zombie Island - A very creative way of getting rid of those nasty zombies! Well done!

The Locked Room Mysteries - A very nice solution!
Unfriendly Neighbours - Oh wow! That 100% solution is a thing of beauty! Brilliant!
These lemmings and those lemmings - Another pair of brilliant solutions! I made the walls exactly 8 bombers thick, so that the player would be forced to conserve lemmings if they chose to use that solution. 8 bombers and 2 blockers on steel means that all other lemmings have to be saved, which can be tricky in its own right.
Crowd Control - A very nice use of the release rate here! I think I may change this level to have fewer lemmings, as waiting for them all to be released is very tedious.
Thick and Thin - Great solution here! I like the acrobatics that the lemmings get up to!
A Sorting Problem - Another great solution! Though I might tweak this level to be a little trickier...
The Big Dig - Solution 1 is very nice! And you even did it with over a minute to spare! Solution 2 definitely seems like a backroute, though. I shall have to investigate...
Equivalent Exchange - Unfortunately, both of these solutions are backroutes. That trick underneath the right exit should definitely not be allowed. Your first solution uses a very interesting trick with the laserers. I had no idea you could extend the horizontal reach with them.
Fun with Laserers - Another very nice solution! However I might tweak this level to be slightly more interesting.
Escape from Zombie Island - An excellent solution! I audibly gasped when I saw the path you were constructing for the builder!

Removed one fencer, added one basher

Removed the aformentioned basher, replaced with a miner

Removed a piece of wire to the left of the exit

You got it!
The original intention was for the fencers to be red herrings. They would be too slow to use and so the zombies would always overrun the lemmings. This would force the player to use the laserer to blast three holes by using the teleporter.

Unfortunately it didn't work out in practice; the fencer is still fast enough by itself. I could simply remove the fencer entirely, but I fear that would make the solution too obvious. I'll have a think, and see what I can come up with.

Once again, nicely done!

Danse Macabre - Great solution. I especially liked how you commented on the date of Feb 14 1991 being the original release date of Lemmings. I think you're the first person I've seen who noticed that!
Pumpkin Patch - Good job on this one.
Feast of the Dead - Good job on this one too!
Knight Time - Very good solution! Was a real treat to watch you figure this one out.
The Heebie Jeebies - A very nice solution!
The Witching Hour - Nice work with this one!
Grave Danger - Great work. I laughed out loud when the first lemming was killed by the trap, because it caught me off guard.
Across the Abyss - Your solution here is spot on, great job!
Poltergeist - A very nice solution! Oh, and a poltergeist is indeed a term for a ghost, more specfically one that levitates or moves things around. Hence all the floating furniture

The Lurking Fear - Another very nice solution
The ol' Switcharoo - You mention in your lets play that this level is very similar to the Lemrunner level, "Switching Gears". You are correct! I consider that level to be a sort of spiritual successor to this one. Great job with your solution.
We all float down here - Great solution! Incidentally, some of the level names are references to famous horror stories or movies, including this one! How many can you spot?
It is a mystery - This is a backroute. I seem to recall this level has a ton of backroutes. I don't really mind all that much, since it's still a very tricky level. Great work! .
I want to get off Mr.Bones' Wild Ride - Great solution
Floating Forest - Another level with quite a few backroutes. This one was very rushed to try and get an october release, so I didn't really have time to playtest it. It probably needs to be moved up in the level rank. Great job again!
It Crawls - This is a very nasty level! I've reworked it to be more forgiving. Great solution though!
Mirror Mirror - Excellent solution! This level was always one of my favourites, and your playthrough of it was a joy to watch.
The Lemityville Horror - D'oh! A nasty backroute! Hopefully I can fix it...

We all float down here - Made the swimmer lemming neutral.
It Crawls - Increased skill counts and decreased save requirements.
The Lemityville Horror - Added metal beneath the floorboards.
Moved the Floating Forest level to an earlier position in the rank.