Shacknews has two articles up on Reach matchmaking and playlists, which explain a couple of the features teased in the multiplayer trailer, Active Roster and The Arena.
Queue-Joining - In Halo 3, it was difficult to join friends that were already playing in a match. You had to wait until they were finished. If you started a game while you waited, they would then have to wait for you. Instead of going back and forth, Reach will support queue-joining. Simply put, Reach will automatically join up as soon as your friends are joinable.
Streamlined Party-Up - After a Halo 3 match, players were presented with the option to "Party Up" and merge lobbies with all willing players. In Reach, it will be an opt-out system. After a match, players will be kept together and it will automatically roll into looking for the next match. The system is flexible enough to allow Bungie to determine, per playlist, whether to keep a team together and find a new set of opponents or keep an entire game together and move onto the next map.
Active Roster - This is a throwback to Halo 2. When you boot up Reach, right at the main menu or lobby, you'll see a list of what your Xbox Live friends are doing within Reach. You'll get detailed information about any friends playing Reach including who they are partied with, what game they are in (plus score and remaining time), and more. Basically, Bungie wants to make it so that you do not have to utilize the Xbox Live Guide to find out what your buddies are doing in Reach.
Improved Voting System - Halo: Reach will utilize a new voting system, which Bungie described as "Veto 2.0". Each playlist will provide players with four options. The first will be a combination of map and gametype, much like you would see in Halo 3. The other three options will offer players additional choices to vote on. Thankfully, you'll know up front what your four options are so you no longer have to risk voting down a favored map, but unfavored gametype and getting an unfavored combination.
The Arena System - A Ranked Set of Playlists for the Hardcore Community
Possibly the largest change coming in Halo: Reach is the Arena. This is a Slayer and Team Slayer set of playlists entirely geared toward the hardcore. If that wasn't enough, players will be rated and placed into skill divisions in month-long seasons.
The rating system is smart enough to realize that kills aren't the only determining factor behind skill. This is especially true for team games where assists play a huge roll. Similarly, players that have a greater kill/death ratio (had more kills than deaths) will rank higher than players that die as much as they kill.
The divisions are Onyx, Gold, Silver, Bronze, and Steel. It is possible to move up or down within a single season. To qualify for ranking, players will have to play a certain number of games a day to gain a "Daily Ranking", which will be an average of a player's best games from the day. To get a divisional ranking and compete in a season, players will need a certain number of Daily Rankings.
Casual gametypes will not appear in Arena playlists. You won't be seeing Rocket Race or Fiesta here.
Even though Arena is geared toward top-level players, it should help less skilled players avoid being matched up against people they have no chance of winning against.
The second article focuses on Arena.
