Save all your incineration cannon ammo until the final platforms at the end of the game. You'll know what I mean once you get there.
There's no need to save any IC ammo, really. After you get it, there's a part with 4 knights, one has an IC. So you can get through that easily and still have full ammo. After that it's only the crawler hell room where there's no knights, and then it's the end platforms.
I didn't think it was that hard, I blew through it in a few hours last night, as long as you don't try to kamikaze everything, the worst part of it all for me was trying to keep enough ammo to take out all the enemies guarding the shield defense button
"Apparently you can have your desire and still suffer terribly for it, a lesson for all who would consider marriage" ~ Morrigan - Dragon Age:Origins