The first section can be divided in five subsections: the paws - the cyan esophagus - the fangs - the two barriers - the final monster. It's the hardest part.
The Paws. They hang dangling from the ceiling or moving from the ground, and sometimes you can't avoid them, so the only way to get past them is to shoot their weak spot, clearly visible toward the "root" of the paws. It's probably the easiest part, besides the power up's portion at the start.
The Cyan Esophagus. A series of narrow passages riddled with little organic excrescences shooting organic bullets at various speed in irregular ways. It's a very delicate moment, the shootings are really unpredictable and can surprise you anytime, while your manoveure space is really limited. At first I tried to get through using a maximum speed, and it was an improvement, but still too many attempts didn't end in a good way. I then practiced a surgical use of the diagonal missiles, shooting each couple of ceiling-ground excrescences, but still wasn't satisfied. The best strategy seems to be mixing the two techniques.
The Fangs. Big white horns or fangs from both ceiling and floor, moving up and down - not difficult as it may seem during the earlier attempts: with care and speed you can go past them without much trauma - although there's the organic excrescence variable looming here too.
The Two Barriers. After a long line of upper excrescences for which you'll need your cut through laser to get past easily, you encounter the first barrier you must pierce through. I had some problems with it, because sometimes I died while wading through it, and I didn't understand exactly why. Apparently the organic tissue reformed while I was still in the barrier, so I decided I have to move through it faster. It wasn't enough, it seems. I have the impression that you have to avoid hitting the barrier before actually be very near it, not even hitting a point you're not going to enter. After the first barrier there are spores of various size placed in the middle of the canal, and the usual excrescences, and then an even larger barrier appears before reaching the final monster's lair.
The Final Monster. It's an ugly thing, almost costantly shooting at you, so you have to move up and down, to avoid the swarms of organic bullets, while the monster tries to adjust his aim. If you have kept your power up's, you're still well equipped, and you stay focused, while costantly shooting - overwhelming it won't take too long.
The other sections are shorter and relatively easier.
Second Section: Asteroids Galore.
The second is a typical vertical dodge-the-asteroids ordeal, with the odd alien swarm here and there. You have just sweated like a lashed Ancient Egypt slave to finish the first section and you must immediately face another traumatically fast and lethal situation; a meteor storm. But there's a trick, I think, and that's keeping the fire button constantly pressed: apparently this cause the movements to slow down allowing you to react more safely to the constantly appearing asteroids.
Third Section: The Tunnel Of Hell.
Fourth section: Technocratic Bowels.
The fourth section is vertical, in a technological environment, where swarms of enemies drop loads of hard-to-avoid organic bullets. The secret is keeping on the left side of the screen, just next to the wall: the aliens won't appear along that trajectory.
Final: Great Balls of Ice.