And now, my thoughts on the set as a whole.
Backroutes on levels 10, 11 (and 15 if that one was a backroute, as I think) need to be addressed.
Level 13 is identical to level 7 minus the bomber. But since neither the obvious solution nor my 100% solution requires the bomber, having this as a separate level seems superfluous.
The order of the levels is mostly accurate. As I said, level 4 should be placed later, and I would place the last few in the order 14-(15)-17-19-18-16. (I've put 15 in brackets because of the backroute; nevertheless, it's good to keep 14 and 19, the duplicate levels, a little bit apart.)
The "scenery" on all the levels is especially well designed, and you have a rare talent for making plausible red herrings out of parts that aren't actually relevant to the solution!
Overall I think that in spite of the backroutes this is one of the best packs I've played. Partly because I'm sick of the way most people on the forum delight in making levels that are way too hard for my humble skills......