One thing to add, achievements that say they need to be completed in ranked or social playlists can't be earned in 7 on 7. (Maybe they can, but it didn't work for me. Specifically the achievement "Blades of Fury.")
Recruit - Onyx
Halo 3 fan who still plays the original Xbox 360 version regularly.
Made your first hot drop into HaloWaypoint.com
View your Service Record on the web.
Become a member of an active Spartan Company.