Wired tackles hidden secrets in Halo 3:

In case you've been living under a rock for the last year, Halo 3 is the latest blockbuster entry in Microsoft's incredibly popular series of first-person shooters. And knowing that every inch of their game would be pored over by Halo devotees for years to come, the designers snuck quite a few secrets into both the single- and multiplayer games.

There's some good info here, including how to find all the hidden skulls, a feature carried over an extended from the Halo 2 days. I continue my slow progress through Halo 3 on Legendary, by the way. What I've found--so far, at least--is that nothing is insurmountable. You just have to take your time, figure out what it is you need to do to get to the next checkpoint, and slog through it. In this way, Halo 3 is like any other shooter on the hardest difficulty level: You just have to proceed slowly and stay in cover most of the time. Right now, I'm about 1/3 of the way through the second-to-last mission, Cortana. You may recall that this is where I had problems even on Normal mode, so I'm being particularly careful. So far so good.