Bungie is making some important and dramatic changes to multiplayer matchmaking in Halo: Reach, with a revamped set of online options that cater to the hardcore (see Arena mode) and new social settings that improve everyone else's experience.
Shacknews has a comprehensive look at Halo: Reach's multiplayer side, which includes "Arena Playlists" targeted at the hardest of hardcore Halo players. Players competing in Slayer and Team Slayer playlists in the Arena will be ranked and placed in monthly skill divisions, a chance to compete with the best but still find matches at your level.
There are still options for the less serious and more casual Halo player in Reach's multiplayer mode, where players can play non-hardcore gametypes like Rocket Race.
While much of Bungie's work on Halo: Reach multiplayer appears to be on streamlining the process of getting in and out of games, some matchmaking work is left up to the player in the game's Social Settings.
Those options include basic settings like connection rate and language, but also give players an opportunity to define their online gaming personality. Social preferences, including a player's tone (Polite vs Rowdy) and motivation (Winning vs. Having Fun), should make Halo: Reach multiplayer a better experience for your Spartan style.
The full rundown is, as we said, comprehensive. Read up in advance of the beta so you know what you're getting yourself into.