I'm in rating 2 level 8: Knights of Honor. So far really enjoyable stuff, I had high expectations for this pack and they've been nicely fulfilled!
So much effort put in every level, playing experiences are guaranteed to be superior to sparsely detailed levels in many other levelpacks. So far maybe even a bit too many too large levels, to some extent it could turn out to be tiring.
In my opinion the difficulty is really high already, and if you compared in your starter post those difficulties to the original Lemmings, then I'd disagree.
I think the game goes Mayhem already in the first rating, 4 last levels were pretty tough. All the levels (except for maybe level 2) have been also Mayhem or higher tier in my opinion in the second rating. So, I don't know
how hard this is exactly going to get, or if the rest of the ratings are going to be close to each other in terms of difficulty.
I love to see the different tilesets though, and there seems to be quite equal amounts of those, which is always an issue I respect a lot.
And did I already mention that the music is splendid too, I feel so pumped up for these challenges with all these new tunes, like used in rating 1 level 28: Morituri te salutant!