Seasons 1-6 used an individually based ranking system where you were ranked 1-8 based on your in-game score. Seasons 7 and on used traditional trueskill where your rank went up/down completely based on if your team won or lost.
As for settings:
Season 1:
Playlists: 4v4 and 2v2
Maps: no killzones on zealot/top Asylum
Slayer Pro-Sprint only
Default Slayer-All Armor Abilities
Season 2 changes:
Slayer pro removed, everyone used camo
Season 3:
Camo removed, everyone used Armor Lock
Season 4:
Season 5:
FFA playlist added
Season 6:
Season 7:
Arena Doubles removed, FFA playlist removed
Ranking system changes, everyone uses evade
Season 8:
Evade removed, everyone uses jetpack
Season 9:
More forge maps added
Season 10:
Jetpack removed.
[Edited on 01.05.2013 4:06 AM PST]