16 "Don't Do Anything Without Thinking" - Sorry, but this is a bad level. It's an example of the levels you might've heard referred to as "builderfests" - levels that basically come down to "hold back the crowd with some trivial means, then repeatedly do the same / very similar thing until you reach the exit (usually, but not always, building and/or platforming)". Think back to Taxing 14 "Hunt The Nessy" in the official game - boring level, right? This one might look different, but it's the same idea - just build, build, build.
17 "Not so easy when you don't know how" - This one is much better, though! However - while this is a pretty good level, it's far too hard for the position; I would suggest moving this to somewhere later in the pack. The other suggestion I'd have here is - most of the bottom is just waiting around. This could likely be cut down significantly - just a couple of traps then the exit, no teleporters needed. The key thing that tripped me up at first wasn't "go back through the teleporters", it was "don't open the exit too early" - and that still works without the teleporters. But yeah, overall - great level here!
18 "Let's block and disarm" - Another not so great one. It's pretty obvious what to do here, and there's a lot of waiting around once it's done.
19 "Provide for my Lemmings" - Another builderfest. Skipped. (Sorry - I've played through too many of these to bother sitting through more than one or two, at most, per pack.)
20 "The Eagle Has Landed" - This one, too, was really just "do the same obvious thing over and over", though at least it wasn't building this time.
21 "You Live With 1" - This one had far more variety, but still, it's just a matter of "whenever you get a pickup skill, use it right away", no real puzzle to speak of. This is fine right at the start of a pack; on the other hand, 20 levels in, things should be at least a little bit more complex than that.
22 "A feast of a level" - This is more interesting! I get the impression there's many ways to solve this one, and there's no immediately obvious "just do this" that jumps out, even though it's still a fairly easy level overall. This was another good one!
23 "T marks the spot" - Pssst, that's a reference to Taxing 17's name, not Fun 23's (which was originally "I've lost that lemming feeling"). ;) Also, the screen start position needs adjusting here - the screen starts focused on the exit, not the entrance. That aside, the first half of the level is somewhat interesting, but the second half just feels like filler.
24 "SEGA Lemming san" - First - PLEASE move that entrance so that it's visible without having to wait for it to open first! If it really needs to be at that exact height for any reason that I'm not seeing - make the level taller so it fits. Also, the preplaced lemming seems to serve no purpose whatsoever - he's just there to let him die. The mass shimmier assignments at the start seem to just be filler, but except for that part, this is a VERY GOOD level - but this is also at least Taxing difficulty IMO, not Fun. It probably took me longer to figure this level out than the rest of Fun 16 - 30 combined, and in particular the way to release the crowd is a pretty advanced trick.
25 "Lemmings Lemmings Not Everywhere" - I majorly backrouted this (unless you intended for this to be an option), though it doesn't look like the intended way would have been particularly interesting either.
26 "Nightmare on WillLem Street" - And a very similar backroute actually works here, too. :P
27 "Don't have to be too careful" - While the underlying idea is alright (though not particularly amazing), there's a lot of issues IMO with the finer details on this one. For starters - why make the entrance face left? All that does is add half a minute of waiting time at the start. EDIT: Scratch that particular point; after taking another look, I see what the intended way here, and left-facing does make more sense for that. However, at the same time, for that route - move the entrance further to the left, or perhaps make the level narrower in general? Likewise, the idea works just as well with only 5 or 10 lemmings; having 30 just means more clicks needed to assign all the permanent skills / shimmiers (and it would be even worse if I had to assign the climbers too - but I found a solution that doesn't need them). But the biggest issue is that 1px gap on the right - on a large level like this, which will likely be played a bit more zoomed-out than usual, that gap is quite tricky to spot until a lemming walks into it. It's not hard to deal with because the player will almost certianly have a spare builder, but at the same time, it also wouldn't harm the level to make it slightly wider so it's noticable. Overall though, this is better than some of the other second-half-of-Fun levels here - it just could use some further improvement.
28 "If only they can survive" - Any level with hidden traps is a terrible level. Don't hide traps (or any other not-purely-decorative object) in terrain. Yes, it was a surprise twist when you encounter one for the first time in the official game. By the time you've played as many custom levels as most of us has, it's just blatantly annoying to run into one. On top of that, all there is to this level is "assign one disarmer to the first lemming". Even without the hidden trap aspect, this would still be a pretty boring and trivial level; except for the disarmer it solves itself.
29 "Worra Lorra Egyptians" - I suspect this wasn't the intended way to solve it, unless it's meant to be open-ended, but this one was a pretty decent level either way. Similar to 27 though, it would have been better off with fewer lemmings.
30 "Unlock your lemmings" - This one's also fairly decent, although again it could have done with fewer lemmings. In this case it does need more than 5 for sure, but 10 or 15 would have worked.