General comments - There is a lot of levels where you can just use Blockers and Walkers to contain the lemming crowd and send one worker lemming. These levels are generally ok if there isn't a lot of them. The best lemmings levels on here tend to be ones where you don't do what the Lemmings designers did with Original Lemmings and Oh No More Lemmings, containing crowd with blockers and sending worker lemmings seem to be the thing they did to death.
Also Time limits are generally not needed most of the time, you should only add time limits to block backroutes which take longer to execute than the intended solution. Time limits are ok if it fits the theme of the level you're trying to go for.
Calm 1 - It's generally frowned upon to put time limits in levels which don't really add anything to the level. Other than that it's a nice first level first rank level.
Calm 2 - The pillars near the trapdoor have very minute gaps between them which caught me off guard, I'm not sure if that's intentional or not but I can see other people commenting on this. Otherwise another nice level.
Calm 3 - Solution is simplistic but the level design is good

Calm 4 - Another nice looking level
Calm 5 - I really liked the look of this level but I felt it was let down by the intense amount of building. It would have been more interesting I felt if one could not bash through the wall above the flamethrower but that's my personal opinion. I get the feeling the intended solution would have been to build around the flamethrower.
Decent 1 - Brilliant level, I liked how the 2 lemming crowds could not join together and the platforming over the traps at the end was a nice touch.
Decent 2 - I felt this was a little too neat for a Rock tileset level, they are supposed to be jagged and lumpy like the Snow tileset I feel, that's my personal opinion though. I feel this level would work better without the platformers and have just builders.
Decent 3 - Great level, this one really got my thinking. It felt like hitting Crazy 1 in Oh No More Lemmings, where have all the skills gone?! More levels like this please! Time limit is not necessary here.
Decent 4 - Great level design, this level was not too bad solution wise. Although the lower block near the start is actually 1 pixel to the right of the upper block, not sure if this was intentional but it wasn't clear to the player either.
Decent 5 - This level could be greatly improved if you made all of the gaps such that they only required 1 builder or 1 platformer. Having gaps which are just too long to make it with one builder are frowned upon generally - either make them long enough such that they require the full length of 2 builders/platformers or make them short enough for 1.
Suspicious 1 - I don't often see ice blowers pointing upwards so this was a first for me. I'm not sure how others would feel about this but it's a nice level nonetheless. Making a good snow level tends to be hard I find so Snow levels will always get a thumbs up from me.
Suspicious 2 - I liked this level again but the building gaps are a bit too long. Long building sections should be avoided in general. I liked the use of the fencer in this level.
Suspicious 3 - Good level but would work better as a first rank level, I'm not sure if this was placed here because the title suggests that you need to take a break in a harder rank.
Suspicious 4 - Here we have a backroute (almost certain), I feel like this level could be good with a bit of tweaking. Also why not make all of the lemmings spawn as Climbers and Floaters. The 15 floaters in the skillset doesn't add anything because all of the lemmings will need them. The prettiest looking level in the pack I think.
Suspicious 5 - This level could do with more decoration, it's a very empty looking level. This level also seems to suffer the most from the Blocker/Walker method I used throughout the pack. It could be more interesting with more advanced containment techniques.
I don't mean to be harsh in this feedback, it will help your levels get better in the long run. I'm just making general observations on what other people will tend to say when they play these levels.