Halo Reach compared to this one was simple because:
Not everything was so clumped up on the screen(which is a big factor)
Not so much text was shown on screen at any given time unless you clicked on something that displayed more information.
When I say "simple" you need to understand basic UI design(the kind you would take in a UI design course which I never took but there is one at my school and my friend would teach me some of things he learned and I would impliment this advice into my games, editing, etc). If you don't understand that then you're going to misinterrupt what I am saying.
Basically: Too much on screen at once. Allow more spacing and options to display more specific information.(I should point out I was talking about the custom game lobby not the whole thing.)