For a while the NL styles had bugged copies of the Basement and Bridge sets (Garden was unaffected). Redownloading the NeoLemmix styles should fix this.
With that being said, the Lemmings Plus VI musics need to be in a folder "Lemmings_Plus_VI" inside the music folder; not in the base music folder themself. The music download ZIP does not correctly reflect this.
I've solved the first three of Nessy's levels.
The main difficulty was figuring out how to control the crowd at the start. I did look at several other possible routes, but only because at first I didn't realise this one was feasible.
I remember having a lot of difficulty trying to solve this level (and might even have given up on it, not sure) in the past, but I actually solved it pretty quickly this time. A nice level.
This one too, I remember having difficulty with, but unlike Crossover, this one gave me a lot of trouble this time too. I did solve it in the end, though - and I'm very impressed with the solution. Simple, yet extremely well hidden.
I've made several attempts at the next one, Odyssey. While I can save a significant portion of the lemmings with the remaining lemmings still alive and safely contained, I have not yet found any solution that actually completes the level.
Solved Nessy's level "Loving the Chaos" that had the missing piece issue before.
Nice, I tried lots of climb-bomb things at first, then a variant of my actual solution that doesn't let the crowd drop to the bottom ledge. When I realised this fell one builder short, I noticed that by using that ledge, I could eliminate one builder from my solution. Upgrading it from "solved" to "talisman" was simply a matter of switching a blocker for a bomber in the top-right.
Came back to Journey, and solved it this time.
The key thing I was missing before was that I was using a platformer to cover the first gap, because builders would hit and turn around. I decided to experiment with builders anyway because my platformer-at-that-point solution was always falling a skill short but some paths left a spare builder, and then I clicked on to the blocker-walker trick. Genius! With that spare platformer, the digger was no longer needed near the end, and everything else fell into place from there.
Completed Swampflower
I have to admit... this one was pretty clever. It's fairly obvious where you have to use the Cloner, but that then easily puts you into a false mindset in regards to who to use the 2 Climbers on.