I've started playing through this and jumping around the difficulty ratings. It's been pretty fun so far, though the difficulty does fluctuate quite a bit.
Troll levels just don't work in NeoLemmix, as I learned the hard way. Pretty much anyone is going to press the clear physics button and then all of the trolling is revealed.
I do like how you put the traps behind the creatures. It just looks neat, even though there are some who I know will hate this. "The Black Widow" was pretty fun to see how the traps were stacked up like that.
I do believe I've found some backroutes though. "Painful Parkour" seemed a bit too easy because I found a way to basically ignore the bottom half of the level, and "Luring Lemmings into mousetraps" can be done by just using a digger near the start and cranking the release rate. I also feel like "Lemming epigenetics" and "Shock absorber" aren't different enough. The reduction in skills for the harder level doesn't really change anything.
These are just some things I've noticed up to this point. Overall it's looking good though!

This was a pretty neat pack. There were a lot of 'contain everybody while you build the path' levels but there's nothing really wrong with that. It just makes everything feel a little bit samey.
Because you have to save less than half in Decent 1, you can just ignore either the top or bottom entirely. Seems a bit odd.
The graphics pieces are sometimes laid out a little bit oddly, like that spot of water in Suspicious 2 that's completely under the ground, yet you can still see pixels of it popping out through the top. There was also the lizard in Decent 2 that had its trigger buried in the ground, thus rendering it useless. Apart from those little things, it looked pretty nice overall.
I was also able to cheese Suspicious 4 by just cranking the release rate to 99 immediately and then starting to bash through the wall. Most of the lemmings will turn around by the time you get through. By doing the same thing with the second wall everyone will turn around. Then you just clone the basher 3 times and you're done. It's even still possible to save the basher by platforming out and then cutting him off with another basher so he can climb out. Still a pretty neat level, and it stands out among the others as being more puzzle-oriented.
I think my favorite was "There is only one way." "Distance" was pretty good too; I feel like with some tweaks it could be made into something very interesting that forces you to use some skills in different ways.
The difficulty curve was pretty well laid out, and though it was overall easy it was still fun. Good job!

I'm a fan of the SNES soundtrack; that's the one I grew up with. The other versions of the original songs sound kinda strange to me.

If I end up making a few levels I deem too hard for Casualemmings, I might compile them into an extra rank called 'Hyper'. Haven't seen that name in the suggestions so far.
Might as well take it all the way with a gradient: Calm -> Nervous -> Twitchy -> Hyper

Just a guess, but it's probably because I'm using namida's updated bubble tileset but didn't include it in the pack. There might be a small difference between that tileset and the default bubble tileset that goofs up that level. I think it's because I tried to add a background object that doesn't exist in the default tileset. You can try searching around the forum for namida's updated tileset and use that instead of the default one. If you really don't want to do that, I can make a quick patch to remove the offending object.

I still think this level pack needs some work anyway. I'll get around to it sometime....

I'd take caution with the stacker staircase idea. It's possible if you interrupt them with walkers, yes, but if you spam it too much like I made the mistake of doing in Lemmings Squared then it becomes very tedious to play. I've been trying to use stackers in different ways in my more recent level designs and have come up with a few other methods to make use of them, such as a level where you use the little bit of height from a stacker to make an otherwise lethal fall survivable. The pack is also using the one-screen level idea a lot; nearly all of the levels I've made for it so far fit on one screen.

I find it especially hard to order difficulty of levels properly on the first try. Many times I've made levels that I thought were pretty simple because they just contain one little trick or bit of misdirection that trips up my testers way more than I thought it would. That's why it's good to have multiple people test your levels out; you alone as the level designer are not going to be the best judge of its difficulty because you know how it is supposed to be done. By the same token you can blind yourself to potential backroutes. That has also happened to me many times.

Thanks for the encouragement. The direct feedback can hurt, yes, but once I move past that it's very useful, so I appreciate it. My first pack isn't all that awful, but it still needs quite a bit of work to make it into something I'm really satisfied with. A lot of the hard levels later on are broken in one way or another, and for some of them fixing it will be quite the undertaking. It's rather intimidating, and I've already invested a lot of time into making Lemmings Squared in the first place, which is why I've decided to work on Casualemmings first. I probably will go about fixing up Lemmings Squared once Casualemmings sees a full release.

As for demo level 6, my solution also has some skills left over. Many of the levels, even the later ones, will give the player more than they need to finish it. I feel justified in doing this because the original Lemmings did this a lot as well. Even the last 3 levels in Mayhem all give you more skills than you technically need to win. Sure, NeoLemmix has space-time rewinds and precision tools to make things easier to aim precisely, but since I'm trying to make the pack more beginner-friendly then I feel that designing the levels like this will work better. It also makes them less susceptible to being backrouted because somebody figured out how to place things slightly more optimally than I did. And I know that will happen because it happened in Lemmings Squared.

Well, I haven't been very active on the forum lately, because I've been working on this. My first level pack left a lot to be desired. I made quite a few mistakes when designing it. I rushed to meet a deadline that didn't exist. I didn't throw out bad ideas. I tried to do too many things at once with it. The levels were not tested well. Most importantly, I lost focus on what I was originally intending to do. The end result was a pack that had a few good levels, a lot of mediocre ones, and quite a bit of hot garbage.
This new pack I'm working on aims to avoid all those pitfalls. It will be an easy pack; I've named it as such to constantly remind myself of this. There will be three ranks, and the difficulty should never exceed late Tricky / early Taxing stuff. I'm aiming to have at least 60 levels in the finished pack, though there may be more. Currently, I have 31 levels built for this pack.
Attached is a demo with 6 levels. Pre-level text describes some of my thought processes for the level designs.
This demo should work with the latest stable release of NeoLemmix. The final version will have custom music and title screen graphics, but I've left those out of the demo.
Enjoy!

Updated to version 1.01; check the first post for the new download.
Changes: Moderate 10 got a graphical touchup (layering errors... ) and new pre-level text explaining the splitter object.
Removed the stoners from Simple 6.
Some additional pre-level text added to explain NeoLemmix objects/skills better.
Talisman descriptions now reference the correct levels.
Talisman requirement for Moderate 7 changed. (All I needed was to be told 100% could be done and I saw how right away. I was just missing one step )
Moderate 17 now gives you far fewer Walkers so you can't just punch through all the walls with Miner/Walker canceling.

More changes will likely come as more broken stuff is discovered. Thanks for the testing help! I still have to sort through Nepster's comments, working on that now...

This is why some people turn to drugs and alcohol isn't it

Talk about a dedication to your craft...

Nice work with the 100% saved, Icho. It's not too hard to do that because I gave you way more skills than you need to actually finish; I took my record for least skills used and then bumped the number you get for each up to the second square above it. The time limit is there to enforce a degree of multitasking; you can do it in less than 8 minutes if you're efficient but if there was no limit you could just do one section at a time which I thought was a bit too easy. What I'm really waiting for is somebody to finish it with less than 204 skills. I know somebody out there can do it.

As for hidden traps, I'm ok with it. The traps in Simple 3 fooled my sister and her reaction was hilarious, so that's why I do it. I'm untrusting and usually tap the clear physics button at the start of pretty much any level, and it's not like you have to leave it on while you play. Just turn it on to see where stuff is or when you're working up close to a trigger. Design philosophies will differ.

Simple 10 and 13 are pretty similar, but at least 13 asks you to do a bit more, like cut off your builder early.

I should add more intro texts, yes. Got lazy with that. Also probably shouldn't have the stoners at all in Simple 6. I really didn't have many levels that use those.

Squared version 1.1 is now out, featuring major revamps to levels, new levels, backroute fixes, and more custom music variety!

I recommend using the latest stable version of the NeoLemmix player to play this. It isn't built for the new format, though I will likely port it over once that format has stabilized.

Link to the custom music: https://www.dropbox.com/s/307whfpun4yf77q/squaredMusic.zip?dl=1
Check the readme file within the .zip if you don't know how to make the custom music work.
Be sure to download this even if you have the old version of Squared, as there is more music now.

Enjoy, and have fun with the backroutes! I'm sure they're there somewhere, still...

I do like the song but I am bothered by this 'joke' because I'd like to actually hear the track I spent two hours mixing when testing my final level instead of this thing. If I never wanna give it up I'll just listen to the full song myself.

Level progress at 94/100.
Just finished designing a custom graphic. The final level is going to be rather work-intensive to design (still have to make the music for it too), but it's just that, one other boss stage, and a few other gaps to fill in before it's ready for a full release.