Great work thus far, of course. I've been going through and there is one glaring omission that I'd really like to see fixed: you should include links to specific times in the youtube videos.
Let's take Halo 4 for example. The only collectibles are Terminals. You'd have me start the video at the top, scroll down to the mission description to get the approximate time, then scroll back up (or to another tab) and move to the correct time.
I'll admit, this is really irritating. It'd be really fantastic if you could simply include links to the youtube video that direct you to the correct time (and I do mean a link - not the video itself). An example can be found in Maka's solution here:
. Look at the link below the video.
I think that would drastically increase the usability of the walkthrough.