It is a great level. Like Andet already said, the level doesn't get boring despite its length.
A more detailed description sector by sector:
Sector main: Its great. That's all
Sector Tower (part 1 "Upwards"): I really liked the jumps with the spring and the iceballs, as well as the ladder jumps. I *personally* don't like the part with the moving platform, because in my opinion those are always too random. But objectively, the tower is a made well.
Sector Tower (part 2 "Downwards and across"): This part is in my opinion the worst part of the level. You don't really know where to jump to and the enemies at the bottom are too repetitive.
Sector Factory: This is a nice little parcour challenge. I don't know if it is just my laptop, but the background is flickering like crazy when you move. Despite from this, I really enjoyed this sector. A little bonus tip for the factory spikes: I use the invisible walls from the "Ambient" objects tab, to make the bottom half of the spikes solid. You will still get hurt, but you don't fall this much into the tile, as the bottom half clearly should be solid.
Sector Room: Nice secrets
. And this is a really good area from a storytelling point of view: The player gets a short break before the final battle starts. Well done!
Sector Nolok: This is actually the most unique boss fight I have ever seen in a SuperTux level!!! The only criticism I have is, that I didn't understand how to win this fight. I went to the end of the level and didn't know what to do. I had to look up the solution here in the forums. But I cannot say it enough: A really, really, really good boss fight. I'm impressed!