Wow, we've exceeded the original game's 120 levels!
Critical Procedures- Now I'm thinking, since there are two versions; I should just keep the required to 58/60 for CP. What do you think?
I think you should still make it 59/60, as it's a neater puzzle that way, and therefore more satisfying to solve, while still not too tough as all four solutions so far allow 59 to be saved. (Your solution can easily be modified for save-59, without requiring the blocker trick I used in my save-59 one-athlete replay.) Don't make it easier just because there's a second version. Lemmings had all its easy versions together, followed by all its hard versions; there's no reason we should have to follow the same model. (It's pretty clear already that we won't, considering Laser Deathroom, Changing of the Guards, etc.)
Similarly, I like "Soulful Bounding Leap" (don't forget to correct the misspelling in the title) but I'd like it more if you required 100%, no other changes and leave both solutions in.
About the difficulty ratings; I noticed you gave 'Diggin' the air' only a 1.5. It's easy to us because we've been playing Lemmings for years. But Unless you have a tutorial level explaining that kind of technique (which I never saw it if there is one); I don't think some one new to the game would figure this one out very quickly. Even when you understand it executing it can be tricky/annoying.
Don't forget that, given the designers' propensity for making incredibly hard levels, the difficulty scale is heavily skewed towards the harder end, so the difference between Fun and Taxing ends up being a couple of tenths. It's a little unfortunate, but if it still allows to arrange the levels in the correct order, that's much more important than the numerical ratings (which are only for list purposes) keeping a smooth curve. That 1.5 seems okay to me; you have only one digger, so what else can you do?
(Incidentally, I think Prelude and Hard to Port are both overrated in the current list.)
Also, Come on down / Rumble should be noted as incomplete in terms of decorative terrain; I'm waiting on more tiles being designed for the Underworld set, or if necessary I'll have a go at making some, because as it is, that set is so naff I can't bear to use it.
Path to Mahimah, You Have to Build, Wreck (I'm fairly sure) and Make You Mine can be rated "X" for backroutes. Yellow Brick Road can be rated 9 (you only get four exploders, how could there be any other solution?) Circular Ruins and Thomas the Climber can be rated some high number, they've both been through a fair few rounds of backroute removal.
Finally... you'd seriously rate Changing of the Guards 2 easier than 1? I still haven't solved it, not counting the backroute you already eliminated.
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Yes, I am still working on Cry for me, Untitled Columns Level (it has a title now -- Seven Pillars of Lixdom) and It's all about survival, so don't add these to the list yet. Sorry I haven't gotten round to them yet; I got a request to make a video walkthrough for Repton 2's Caverns scenario, and that may take some time....