I wish Countdown was the answer, I actually thought it would be my favourite game mode pre-release. Having one life is great, it is the single reason I had high hopes for this game mode. As a comparison, Hardcore Search & Destroy is the one thing that brings me back to the later COD-games, it turns the game into a very exciting stealthy objective based shooter.
My problem with Countdown is that it severely limits the maps and funnels players into single objectives from an easily predictable direction. They are not really methodical fights, they are instant gratification standoffs where the attacker is right on the doorstep and you resolve combat in seconds or minutes. While it is not the sprawling chaos of flanking maneuvers and daring assaults you see in Territory, it is still an intense assault mission with more restricted movement and objectives.
Countdown to me feels more like a game of dodgeball than a tactical firefight. It's strongest merit is that it works really well with a small number of players. This however makes it feel more like a game than a battle
A minor nitpick is that the pause between each objective is a big immersion killer. Everytime an objective is captured the game pauses and you see the overhead view of the battlefield. To the player, this is the same as the "game over" screen, the mind starts relaxing and takes you out of the game. This constant starting and stopping is actually a bit taxing on the brain and makes the game mode very unattractive and uncomfortable to play. If countdown is supposed to be a push to take the map faster than your enemy, it should be a constant push that doesn't end until a victor has been decided.