Newborn
Home a-stone - this one's difficulty is a little bit higher, and it teaches you a nice stoner trick!
Tearing Up Brevon's Wires - I don't think the unlock buttons were necessary in this one.
Triple the Puppies - very nice way to introduce cloners and floaters!
Let's Walk Home For Some Rest - nice way to introduce walkers, and that you must only release the blockers when it's safe to do so.
Today's Lesson - nice introduction to locked exit/unlock buttons, and the solution isn't trivial@
Emergency Bombers - haven't beaten this one yet, but I would add even more walkers and blockers. Otherwise, the level can get frustrating.
Gravity on the down low - one of my favorite levels, very nice way to introduce updrafts!
Weird Energy - nice way to introduce slowfreeze, this object can be extremely hard to work with.
Make like a banana and split - awesome splitter tutorial! It's good that you suggested that you hit the Esc button after saving 30 lemmings in the pre-text screen, though in my solution I had to hold on the spacebar until every lemming exited.
Shady Business - I think this level's hard for Newborn. It'd probably be better in early-Hound due to the small skillset and planning how to get rid of the zombies.
You dropped these! - I don't think we need a pickup skill tutorial level since all the other levels use them a lot. Very clever level with a lot of thinking where to use each skill, though this one is too hard for Newborn in my opinion as well, and would also be much better in early-Hound.
Skills built in! - yay, nice to see the remake of my Lemmingbytes level!

Very good level too!
But first some training... - this one is much easier than Newborn 17 and 18, but a nice way to end the rank.
Puppy
Make Sure They're Okay - the exit is not set to No Overwrite, which obstructs my builder as you can see in the replay. Otherwise a good level, though I didn't use the walker.
Police To Meet You - even if this level is in Puppy, my solution feels backroute-y.
Aw Jail No! - nice non-trivial level. I could see this in early-Hound due to the limited skillset and some planning required.
Hit All The Targets! - wow, this one was a little on the tough side due to the limited skillset and the huge size of the level! This might be better in Hound.
Skype Battalion - nice pun! Loved this one as well, especially how you need to plan how to get rid of the zombies! I'm not sure if this one would be good in very-late Puppy to early-Hound.
Hound
So That's Where I left them... - great level, though there was a lot of long walking which made me hit the spacebar a couple of times. It was great how you made the last part with the platforming to the exit lenient, in that you can allow the crowd of lemmings to fall without splatting and giving one lemming time to platform to the exit.

Oncoming Contact - hmmm, is this level possible? I don't see any way I can contain the lemmings, especially since I have to save them all and the release rate is 50. Were the entering lemmings meant to be walking right or left?
Turn around they said... - this one is a major backroute.
FREEZE! - only an attempt replay. This one might be better off in Alpha or Super Dog.
Trapped in no hideout - a very good level and clever usage of stoners! It'd be better off in early-Hound, the solution is not that hard to figure out.
Alpha
No miss hero pants in sight - I remembered playing this level. This one is much harder than it looks, especially with the limited skillset.
+5 Level - haven't beaten this one yet. I'm not sure if this level is possible at all, seeing as the lemmings cannot swim past the waterfall and they get stuck at the top of the pipe, and I see no other way around.
Deploy our Sky Battalion - only an attempt replay. I remember beating this one though, but I need to find my old replay of the level.
Super Dog
Pick Up the Pace Miss Hero Pants - another very good level! I remember watching part of this in a RTW stream. I didn't like the part with the boulders at the beginning, you have to time it so only nine of the lemmings are killed and one must be a blocker, and it may be trial and error to some people. Everything becomes straightforward afterwards, though.