New Features:
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.
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.
Arena Playlists - 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 other 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.
Ranked and Social Combined - Since the hardcore will be in the Arena, Bungie doesn't want to further splinter the community. In Halo 3, Ranked and Social playlists served two different purposes. Ranked games were generally of a higher quality, while social games were more casual.
