I've been doing all kinds of things with Perfect Dark. I won't name everything, but...

I've gotten gold medals on the first ten weapons in the shooting range. The difficulty for doing this varies considerably from weapon to weapon.

I've given them several tries but, believe it or not, I still haven't beaten the third stage of secret agent, or even the first of perfect agent. Those difficulty levels indeed seem substantially more difficult than agent level.
I LOOOOOOVE Flying Omelette!!
Crawl and 1000