Classic 3 - this one is meant to be tight, but with 3 floaters it's not as tight as it was on the video.
Classic 5 - There is an easier solution for the final bit, but requires a little more setup.
Classic 6 - The 2nd death is meant to be in the water, looks like I need to remove a builder. Feels a bit too precise though, so I might alter it again before the end.
Classic 7 - Nice solution, but it was a backroute like you suspected. I'll have to change it because of the threat posed by a no-death solution.
Classic 8 - I did not know about the fire jets, I was as surprised as you were when they built straight through. The level title comes from Doom 2, and the trick needed in this one comes from the original L1. (a whole level was dedicated to it there, then it was used again a few levels later)
Classic 9 - Sometimes I can miss obvious things like that...a bit of metal should sort it though. (and you were correct, the aim is to use the athlete at both ends)
Classic 10 - Part of the problem you had here was that you used a savegame with 60 lemmings. The level is set up for 51 lemmings (becoming 50 when the first is blown up), hence why there are 10 climbers/floaters (only 5 lemmings per trapdoor instead of 6). Some parts of your solution made more sense than mine though, so I'll change some skills around to support it.
Medieval 2 - I only added that hill for scenery, looks like it'll have to go again.
Medieval 3 - Ugh, how the hell did that get there? That looks like a mess left behind after the last update, luckily it exposed another flaw...namely having too many stackers/miners. The level is designed to showcase various roller tricks, when cleaned up it should be fine.
Medieval 4 - Another backroute, some metal should sort it though.
Medieval 6 - I actually forgot that trapdoor was there...I put it there so all 60 didn't have to use the catapult, I guess I can move it closer to the dungeon.
Medieval 7 - Building up a bit higher would've removed the need for that attempted save with the archer.
Medieval 8 - Didn't think the middle trapdoor could rescue themselves...needs sorting.
Medieval 9 - The reason it appears repetitive is because you used precision stacking on each floor (which I would never ask for), without that it's a number of different solutions for turning round on each floor.
Medieval 10 - This is one of two where the time limit is anywhere close, my PB is something like 2½ mins left. You're probably right about the savestate thing, these 10-trapdoor levels do remind me a bit of the larger L3/QFK3 levels, which I would never attempt without savestates. (btw this is the one I'm least happy with, I need to think of some way of speeding it up without breaking the main principle)
Egyptian 2 - You did indeed manage to cheese it. (and missed out on a great puzzle, as a result)
Egyptian 3 - This one was originally more complex (using carpet/shimmy trickery to help stomp down pillars), but dropped all that to focus on the awesome main puzzle.
Egyptian 6 - The basher stuff wasn't intended, the correct way is to fill the other pool of water and bash onto that.
Egyptian 7 - The only thing you missed was an easier way to do the lower glue bridge (no need to pull off that difficult carpet move).
Egyptian 8 - Silly mistake from me to leave that open, esp. given that one of the puzzles is the very same thing.
Egyptian 9 - Couldn't have seen that coming off a sand pourer. The solution? Remove all sand pourers! (I was only using them to turn round, easy to compensate for)
Egyptian 10 - You actually had the correct solution at one point (stomper+glue), but you didn't have another stomper left to finish it off. (I know very little about L2 glitches, so I wouldn't have thought of the basher trick you used instead)

A. Vertical arrows in the ground.

(whether that's a good or bad thing I dunno, we'll see how the Sports tribe develops with it)

Circus 2 - there is a quicker way to do it.
Circus 3 - definitely a backroute, albeit a very clever one.
Circus 4 - I've seen a few backroutes around the exit, but they all have a bit too much precision. (it's kinda hard to prevent them though)
Circus 5 - I kinda like both routes, but the alternative one (which you did) does leave the cannon bit until last, which is a no-no unless you have huge amounts of time. Not sure if I should block one off or not.
Circus 6 - ballooning over the pit is a lot easier than up through a laser hole (and still not the intended route - but again, as you mentioned earlier, these levels are more open-ended)
Circus 7 - one of my favourite puzzles. The reason I add so many twisters (unless it breaks the level) is because they're so unreliable and fiddly to use.
Circus 8 - oh dear, that's embarrassing... (can be easily fixed though)
Circus 9 - another backroute, but can also be fixed.

Highland 5 - for some reason, everyone who tested it so far found the more difficult top route...luckily I was able to fix it in 5.0.
Highland 8 - I forgot about that glitch...even though it's escapable, adding an extra minute won't hurt.
Highland 9 - looks like I have another backroute to fix in the middle, as the rock climber is indeed meant to come from below.
Highland 10 - it's a bold concept and by nature will have many solutions, but I really do like it. Your solution was quite impressive too, but I think I can force the other twister to be used in the intended spot.