I could see a good player doing level 22 no problem, my idea to deal with the huge driller room would be, when you go into the room with the invulnerability and the 3 red hulks, take out the hulks quickly and then use your invulnerability to go down and take out all the drillers. The spiral shaft is really easy if you do it right -- my suggestion: take out all the mine-laying drones first from the bottom, go grab the cloak in the blue area for the way up, then on the way down put a smart missile on each ledge to take out the drillers... there are a couple of secret doors part of the way down with more smarts to refill, so you should have enough.That said, if you don't have a plan it would be hard. You need a plan for that level on any difficulty.