Another tidbit about Halo 3 is a cross-section of a transition in games.
The shipping game just had the combo of skill level + XP = your rank. This was pretty much Halo 2 with a little extra slathered on top.
Then CoD and WoW really hitting it's stride made XP-based leveling more popular. While you did keep earning XP in Halo 3, at some point you would stall out or max out and the ranking system pretty much became irrelevant to you after a few months. These other games constantly had a barometer to tell you the relative investment levels of players.
So in the big Title Update, Halo 3 added Playlist Ranks, which were purely XP based, and made them the rank displayed in the lobby. Not only did this address the issue of people wanting more regular rank indicator, this was actually a pretty good way of eyeballing someone's familiarity with the game. Even if someone was a rank 20 in a playlist, if they were a playlist Captain I knew they would know how to play. If they had a low playlist rank, then I knew it was time to get ready to be a bit more patient with them. It became fun to chase playlist ranks - I eventually got to Playlist General in Big Team Battle.
It was, functionally, like you never stopped ranking. General was 500xp, and you only got 1xp per win in regular playlists, so getting 500xp in every single playlist was basically impossible for 99% of the population legitimately.
Party Chat becoming a thing was also something that landed during Halo 3's life. The game shipped with in-game voice chat, but you had to Push To Talk for any game where the team size was > 4 players, for bandwidth reasons. We lived with it because at the time, you could only voice chat with one other person. Way later they notched it up to 6 people, so you pretty much only had to PTT in BTB.
There was a lot of proxy shit talking and abuse (that I won't miss and don't hold up as a bonus of proxy chat) but also you could talk to randoms that wanted to talk and overhear other teams talking to each other. Then Party chat releases. Obviously BTB teams preferred party chat because 1) it sounded WAY better 2) no more Push To Talk. You could also talk to friends while they played other games, allowing clans and friends to chat without all having to be in the same game.
This absolutely killed off social chatting in Halo 3 in it's twilight years - you never heard anyone anymore, not even overhearing other teams. Hell, since Halo 3 wasn't "party chat aware", you could talk in party chat while the game still let you hear the other teams over proximity chat over your speakers, so it was like Gamesharking your strategy. It also somewhat had a promixity result of reducing Halo 3 population because to talk to people, you no longer had to play Halo 3 together. I could be playing Halo 3 while someone else was playing UNO and another was playing Chessmaster. The sort of "playing via social momentum" ended for a lot of games when party chat came out.
Also, Halo 3 single handedly killed off in-game TS ranks in most of the gaming industry. Halo 3 had a GIANT black market fueled by visible and easily influenceable skill ranks,
even driving me to write this obituary for 1-50 on HBO a long time ago. It negatively impacted the game for even non cheaters due to constant smurf accounts and cheating and boosting going on. After we had lived for years with Halo 2 where people barely played Halo 2 instead of "chase us in the skybox", Halo 3 fixed the in-game cheat issues but not the social ones.
It was so bad that Gears 2 even patched out 1-50 mid-release and went to a pure XP based visual rank system. Obviously all these games used TS under the hood, but I don't think Call of Duty was the main reason here, but just the severe extracurricular market and the negative impact of such on Halo 3 was the canary that made developers and communities want to get away from it. Know why a lot of console games require you to play a minimum amount of games before they even start showing you a rank? Halo 3. Know why Smash Brothers Brawl and U didn't have visible ranks? Literally due to Halo 3 - the developers stated they didn't want people to try and cheat to get a rank.
It was a learning experience for both Bungie and the entire industry.
Also, looks like I'm doing Mega Post Anniversary in here due to this.. lol.