Metal Gear Online got a server-side update today which added a new free gameplay mode. "Team Sneaking" pits one team, equipped with Stealth, against another team which is defending a target. Stealth'd players can be spotted, like in the single player game, and will then be visible until the caution meter goes down. We only tried it out a couple of times, but "Team Sneaking" games seem to go by quite quickly.
A new ruleset has also been added, which can be played in most of the game modes. The name of this ruleset, "Headshots Only," is pretty self explanatory. Any non-headshot kills suffer a points penalty, which makes the game that little bit more interesting. These additions are only the beginning -- no doubt we'll see more added before too long.