Colossus 10 frustrated me for one reason: I figured out its weak spot, hit it with the appropriate weapon, and it didn't react. I have no idea why, but I'm fairly sure that I hit it dead on and didn't get the required reaction. That made me give up and try something else for a while before trying to hit that spot again. It worked the second time, and soon the beast was dead.
For what it's worth, the real hint for Colossus 10 is in the text after "Thy next foe is..." before you start. Read carefully.
Colossus 11 was fun. I was pretty pleased with myself for guessing the right approach early on, but I used the wrong "fall". Once I tried the other direction, it was cake.
Now on to Colossus 12.