The Call of Duty series is one of the best multiplayer games of all time, but it still suffers from major issues. There are a number of things that can be done to improve multiplayer, including balancing kill streak rewards and perks and making sure maps are neither too big or too small for the specific operation.
But the number one thing plaguing multiplayer is the number of times a session is ended because a host ended the game or connectivity was lost. Let's face it, some pinhead leaving the game because they can't handle a beatdown by a rival or they just died in the final match of a search and destroy mission shouldn't wreak havoc on the entire session.
And there's no reason why this can't be fixed.
Taking a page out of business networks, the simple idea of a primary host and a secondary host could easily do the trick.
The best option is to have the secondary host keep up with all the information and then kick in when something happens to the primary. This transfer might not be seamless, but it's better to have a slight pause than to have someone with 29 kills lose a FFA match because someone got frustrated and pulled the cord. However, this would require a slightly larger load on the primary as it must exchange a bit more information with the secondary host.
Another option would be for the game could do a partial reset when the secondary host becomes the primary. Everyone would go to respawn locations, but they would keep their kill/death totals, and the game would keep the main session statistics, like the score in Team Deathmatch/Headquarters/etc. This option wouldn't require any extra load on the primary and would still be better than just ending the game.
In addition to having a primary and secondary host, the game could track the number of times a player left a game, left a game as the host, lost connectivity and lost connectivity as the host. This information could not only be used to choose the best host, but also be displayed on a player's profile. The mere fact that the number of times they left a mission is displayed to the public might be enough to curb some of the behavior.
Whatever the case, Call of Duty: Modern Warfare 2 should do something to provide a more reliable multiplayer experience. There is no reason why anyone should suffer through four or five straight sessions with host ended game or connectivity lost issues ending each session.