I personally enjoy Rapture and Salt Factory, hence why my chapter will mainly consist of levels made with those tilesets.
The End is also pretty interesting because it features the rotating sawblades but it also has some extra obstacles found in it, such as the disappearing blocks.
Forest is my least favorite mainly because all levels made in it feel samey after a while. There's only so much that you can do with only sawblades and fire. Hell, you can't even have keys and locks in Forest. Also, you have to work really hard to make them look good, which doesn't make for a good tradeoff to me.
I think on top of the points you made (which I totally agree with), there's also the fact that the tiles in it are a little disjointed when used together... there's the usual forest stuff (dirt, grass, rocks) and then there's the wood stuff (those slats and thin edges), then
there's the metal factory-like stuff.
When you add them all together, I find it frustrating to make a good design from the combination. Plus, I will be scarred for the rest of my life from making all the dirt tiles by hand in Sandy Mountain... idk how many there were but it took about a week of doing it for hours at a time.