I tried some of the levels today. Before the feedback on the individual levels, two general remarks:
1) You force people to download a 102MB game, consisting out of 2MB actual game and 100MB music data! Pretty pretty please split it into two parts with a big music file and a small games file. With my non-optimal internet connection, I waited about 15 minutes before the download was finished! On top of that, I have to say that the remix music is absolutely not my style...
2) Make double sure that all objects (except perhaps some water) is set to
no-overwrite, e.g. the pickup skills in VM5 or the exit in BH5. People want to see the stairs they build.
So now for the individual levels:
VM1-5: Good introduction levels. There just are a few places, where the lemmings need to walk a long distance and the player has to wait and watch. I find this slightly annoying.
VM 6: Extremely long builder stairs. I will not solve this level and wait for the cheat code to continue with VM.
BH 1: Good level. The only drawback is the first miner+last builder, which have to be placed pixel-precise. I temporarily was under the impression, that the last builder cannot fill the gap and my solution therefore cannot work

. Come on, this is the first level in the second rank. Is it not possible to give players a bit more leeway with the execution?
BH 2: Good short level. (Hopefully this is the clockwork level. Otherwise swap my comments for BH 2 and BH 3)
BH 3: I see only two traps, but somehow three lemmings died? IS THERE A HIDDEN TRAP???
BH 4: A nice clever level

. Problem is again the last builder/blocker (similarly to BH 1). Is it not possible to make the last house slightly longer to allow for more leeway when placing the miner?
BH 5: Without already
knowing the correct placement for the long stair, one spends 100 tries to figure it out

. Please give us either visual hints, or make the required stair much shorter.
N1: The idea is excellent

. However the completely unnecessary trouble with the correct digger placement takes away all the fun. The first three diggers have to be placed pixel-precise, with essentially no way for the player to know this beforehand. When placing the last digger, one often creates a holding pit for the lemming horde. Given the terrain-object overlay at this place, one cannot even properly plan the correct placement in advance, but has to try and try and try...
Overall impression: You have some very good level ideas, but you really have to take into account that players will NOT place skills perfectly and therefore allow for some leeway whenever possible.