Wow, lots of replies!
I've played all four of your levels and I'd say two of them are Tricky difficulty, while the other two could be in early-Taxing.
Great! That was around the difficulty I was hoping to make. I figured I'd keep it simple at first. There's some more specific strategies I had in mind but maybe that would be a good thing to do for a Mayhem / Taxing version of the same levels? (like how the vanilla game did a couple times)
Measure Once, Cut Twice - interesting level in that you have a 2-minute time limit. I'm not sure if my solution is intended
Your replay is really close to my solution actually, I was able to save some builders but my run was slower.
One Way, Another Way - that level reminds me of Mayhem 6 "One Way Or Another" mainly because they're both dirt levels and the titles of both are very similar. It is mostly a builder level, but I like the way you have to save the left side - build a safe bridge using a lemming from the right side so the left-side lemmings won't fall into the abyss.
It was actually inspired by "One Way or Another", that's one of my favorite levels! It's intended to be a mix of Mayhem 1 (Steel works) and Mayhem 6 (One Way or Another); in fact some of the tricks on this level I used for my solution for Mayhem 6.
Watch that first step! - this level is interesting because it has no diggers, and uses zig-zag miners to go down the dirt instead.
I probably should have upped the number of lemmings you needed to save, maybe this would be more interesting if you would have to start out with a low bridge so you could save the lemmings coming out of the right door sooner?
The Dynamic Duo - now this one is the hardest of the four, as it has a 1-minute time limit and a small skillset. I thought the solution was very clever in the end, though I'm only left with one miner and one digger. Best one of the four!
Nicely done! I like your idea
The NeoLemmix Community Pack is in need of some easy levels, and your levels could work for that. 
Sounds interesting, anyone's welcome to use my levels for a pack if they like
I cheated a bit on 'The Dynamic Duo' first time round by slowing the second lemming down, but I did do it properly eventually. I wonder if that level is actually eligible under the current Level Design Contest rules?
I didn't know about the contest, I had a couple other ideas for 2 lemming levels
Also how did you slow down the second lemming? Was it by repeatedly using bashers in thin air?
By the way, "The Dynamic Duo" was inspired by a solution I came up with for "The Great Lemming Caper" (Mayhem 13)
The only criticism I'd make is that, on "Measure Once, Cut Twice", the hatches are right up against a similarly coloured patch of terrain, and it was annoying having to work out or guess exactly where the terrain ended.
Good point (I probably missed that because I usually dug farther to the left), I'll avoid doing that from now on.
I redid the levels and saved replays
All basically the same solutions as I used the first time, except this time with a bit more care I saved 78/80 on "Watch that first step", which is probably the maximum.
Your One Way, Another Way solution was very close to mine, I was actually originally intending for players to spiral staircase up the right side (I didn't think of mining through the terrain on the right to allow lemmings to fall down the right side for some reason); I'm not sure how I missed that you could just dig then mine (I feel a little silly now)
The "Watch that First Step" playthrough was close to what I was intending, at one point I considered setting it up so that the players would be forced to build a lower bridge to save the lemmings from the right door sooner, but I wasn't sure if it was a good idea so I padded out the lemmings count a bit and added more skills and time.
My solution replays are attached to this post 
Measure Once Cut Twice: That was pretty much my exact solution
Dynamic Duo: Very cool run, I like the way you used that digger / miner at the end to get around the trap
I think you're right about the timers, originally I experimented with a tighter time limit for the marble level but it seemed more fun without it (the short time version required extreme precision with builder placement and miners, which just meant you had to play it over, and over, and over... )
The levels aren't too hard, but much fun! 
Measure Once, Cut Twice: The easiest of the four levels. I would prefer to have the screen start at the right end of the level, so that the exit is visible right from the start. Otherwise a very good level.
Very good point, now that you mention it, I'm not sure why I shifted the camera over.
One Way, Another Way: I am not too happy with all the building required to solve the level, but given the various places to use terrain removal skills the level was still fun.
Yeah, I went overboard a little, I sort of wanted a longer version of "One Way or Another", I think next time I'll incorporate more of "Watch out, There's Traps About"(Taxing 2) instead of doing something that requires so many builders.
Watch that first step!: Interesting level. I am only missing a bit more decoration like grass on the earth, ... Currently the level looks a bit bare.
Good point, I probably need to do more detailing in general
The Dynamic Duo: Nice level, even though my solution is probably not exactly intended...
Nope, that solution wasn't intended, whoops! I'll have to think of a way to prevent that.
Thanks again for playing!