Retro 1 Nice first level to the pack - not too difficult but not a pushover either. The worker lemming (or rotten egg) needing to take the top-route rather than following the same path the rest of the lemming would take was a good detail.
Retro 2 Nice semi-open ended puzzle around containing the crowd. I was convinced a save-all solution was possible here, and eventually found something that worked using some blocker trickery at the start.
Retro 3 Good early level, saving the climber using a basher was a nice detail though the timing was a little tight on my solution.
Retro 4 Nice builderless level! By bumping up the RR I was able to save a 2 miners which I imagine are required to do a bit more crowd control if you don't do this.
Retro 5 A nice challenge to try and save as many as possible here with an open skillset. I managed a save 29/30 in the end but I tried for a while to get a save-all by using the builder + digger + builder trick to turn a lemming around, but couldn't quite connect back to basher tunnel without running out of skills to get back up.
Retro 6 Nice puzzle with two distinct workers meeting up - not too hard but satisfying to solve
Retro 7 Very nice idea with re-using have all the blockers get freed to become blockers a 2nd time. The terrain hints to place the blockers was a nice idea to reduce execution complexity on this one.
Retro 8 I like these sort of levels where it is about efficently solving a seemingly simple looking terrain area. It wouldn't surprise me if there more than one solution to this given the skillset and terrain shape, but I settled on an approach using two different digger pits.
Retro 9 I really liked the multiple workers interacting on this one, and the timing with the icicle was very satisfying when it just worked out
Retro 10 Very clean solution, and very clever. The top-left hatch was probably the area I wanted to build bridges with the most, but the solution cleverly requires patience with this hatch in particular. I really liked that no timing was needed in the solution to this level - I did initially think the solution might involve 6px steps around the bottom hatches and some clever timing, but those solutions all ran out of builders.
Retro 11 Another very good puzzle. I found this a little easier than 10 but that's probably because I spotted how to handle the bridge area quite quickly fortunately. Not using a blocker to turn the miner, which is the initial temptation for this level, was a nice twist.
Retro 12 This is a beatiful solution

and probably going onto my LOTY list. There is some very nice subtlety to where you need to place the skills on this for it to work out, and when they are placed correctly everything clicks into place in a very satisfying way. An early solution I had that didn't quite work (but thought it might have been the trick) was to put a builder ontop of the walkway after the exit to turn the lems around - I was quite pleased with spotting this as I thought I had to the key to level, but nope.