CoD4 had (gasp) actual grass you could hide in, and many pointless areas that enlarged maps artifically. This was bad for game flow, but good for, well, chilling out.
MW2 had more mid to large sized maps.
MW3... yeah.
These maps are definitely on the small side. For that, they have good flow, good cover, and multiple routes in and out of almost anywhere, but they are definitely designed to create a lot of conflict at almost any central point on the map and have few out of the way areas to take a moment to breath.
Me personally, I vastly preferred MW1 and 2s maps to BO or MW3. BO2 is somewhere in the middle for me. They're mostly good maps for a style of play I don't enjoy quite as much, but still preferable to MW3.
Anyway, all that said, take an AR or an LMG and slap an advanced optic on it and you can definitely mow people down at a distance. The SMGs are quite terrible at range, so as long as you can catch the runners before they can close the gap, you can come out on top. This is much harder without real friends to cover your flanks though, because there are damn few spots that you can hole up safely.
Speaking to that, unlock Scavenger and take Claymores or Betties with Shock Charges or Trophy System along with a Guardian and a Sentry and you can create your own little fortress of solitude in certain areas.
