Alright here is some more feedback. Warning: I will only focus on flaws here to help you getting a better feeling for level creating.

I think more general advice on what can be improved is the best way here instead of going over every single level in detail, so here is what caught my eye:
- The most important thing: Most of the levels feel really empty and lack any kind of decoration. This often results in landscapes that seem really thrown together. An example would be the very first level (or something like rank 3 level 9): No decoration, just a few steel blocks. The solution may be nice, but it could really use a decorational makeover. Also the radiation is when it's used often spread all over the place. Improving the genral structure could really help.
Compare only the general appearance and looks of the first level to something like this:


Appearance really makes a huge difference, even when it takes a longer time period.
- A lot of unnesseary timers. This seems weirder when I realised that in the first rank you made good use of the timers using them only where they are needed and used the unlimited timer as standard. In the future ranks the timers really got a bit on my nerves, still enforcing the same solution I did with the exception of finding the right time to turn the release rate up. They don't add to the level's difficulty, too. Examples: Rank 2 Level 9, Rank 2 Level 8, Rank 3 level 8 .....
- A point partly connected with the previous one: A few levels have too many Lemmings! Example the first level: Why would you need 200 Lemmings there? Why does Rank 3 level 8 need 100???
- A bunch of levels rely heavily on building giant bridges. Often a 1 or 2 builder gap could have done the same as a 6 builder gap.
- Rank 1 Levels 2 and 9 were with the exception of the last builder placement (also those 1 pixel troll gaps are not relly adding anything to the level) the same level.
- A lot of the levels name were let's say a bit monoton: Ease Way, Smart way, Best Way, Hidden Way, Magic Way, Missing Way........come on a bit more imagination here

Hope my feedback and suggestions are helpful for you!
