Rank - Rank as you knew it in Halo 3, is dead. The concept of Rank has been revamped and divorced entirely from Trueskill (more on that in a few paragraphs) and the concept of EXP (at both the Global and Playlist levels) has also been discarded.
In Halo: Reach, Rank is a global, cross-gameplay-mode-encompassing representation of the time you've spent in the game. So whether you're a Campaign-only guy, or a Matchmaking-only girl, or you swing both ways, you're going to be seeing that Rank advance as you keep playing.
It's about god damn loving time. I hated Matchmaking, I only played custom games and got stuff for it.

Neat.
Indirectly, however, we fully anticipate an acceptable delta in Credit earn moment to moment between good players who win regularly against a guy whose never played Halo before.
Finally.
Q. Man, I can see it now: Part Two. People are just going to sit on their pile of Credits until they have enough to buy the top tier in every category. What are you gonna do to stop players from saving instead of investing?
A. Saving is an Investment in your future.
Also, that player is going to look hysterical, default armor everywhere except for the REDACTED.
Hahaha. "REDACTED".
Q. I am not putting anything on my Helmet, I don't want to increase the hitbox, I'm afraid of conflict!
A. Just like Halo 3, whose curiously sized helmets didn't change the geometry, we're applying the same rules to Reach's vastly expanded customization. If your preferred Helmet has a camera on the side, that helmet camera won't increase your hitbox. Relax.
I was SO SICK of hearing players bitch and moan about "I ONLY USE THIS HELMET TO CHANGE HITBOX LOEL".
Q. Why do you hate Elites? You’re just saving the big Elite customization reveal for later, aren’t you?
A. It's not hate, it's a different kind of love. Elites will be customizable, but not in the same way as the Spartans. Spartans have their own dedicated massive part of the UI, you'll be able to customize your Elite, but it won't be the same as decking out your Spartan. Your Spartan is your identity in Reach.
Where's the elite love :(
Well, this is looking pretty good. A different kind of Halo, which is pretty neat.