I must confess, I never fully played any single player campaign of a First person shooter. They bore me: Hurgah "insert origin of an actual crisis country" mad "scientist or military guy" "kidnaps or creates" superdupermultikiller-"weapon/virus/deathstar", Hero comes to save the world and do primitive jokes. Booooooring. ^^
When it comes to the compatibility of these games, so I dont know the metro you mentioned. (As long as you dont mean the BF3 map. ^^) but when it comes to Halo I do not like that science fiction setting, but prefer "reality" shooters. About CoD its simply too fast and confrontation oriented for me, so its spawning, pushing forward, seeking confrontation, either dying and new spawning or pushing forward, seeking new confrontation. Battlefield is preferred by me because its because of the huge map and allows more team tactic planning, so you can have without probs for minutes no confrontations, and still actively work on achieving your goals. So not shooting, if it fits into your team tactics, can be just as important as shooting. You can be the leader of kills, but if you are in fact the idiot, that spawn by the squadmember that was chosen to be the spawn back up mate and immediately shoot around, without caring to tell enemies about your backup spawns position, you become the idiot of the day, anyway how much kills you have.