The map is very literally your weapon in Modern Warfare 2.
Modern Warfare 2 and the other Call of Duty games have always been very map-reliant multiplayer games. The series abandons traditional design elements like "Race to the Gun" and emphasizes a more tactical, map-reliant approach. This isn’t really intended to be a strategy guide but rather just a discussion about how the gameplay works and feels overall. While I personally prefer lone wolfing it on Team Deathmatch, other players have different approaches and tactics. I talked with several much more advanced players than myself and relied on a couple of different gamefaqs to balance out my perspective. I also don’t really go into team play because I know nothing about it.
Generally speaking, the "Race to the Weapon" design in something like that of Halo 3, adding a layer of strategy for both good and bad players. Knowing the map and where your favorite gun drops are is essential, but for the bad player, there is always the chance to snatch the weapon before your opponent gets a hold of it. This lets that player take the advantage by forcing the player to use a weapon that they’re not quite as skilled at using. Modern Warfare 2 completely ditches this approach. You get to pick your starting guns and can change classes after death. Since players can carry two guns, they usually set up classes that balance out their range payload. Snipers equip something short range for moving from point to point as the secondary, somebody using the SCAR-H compensates for the short clip with a perk or a machine pistol. All the perks and upgrades make it possible to create this finely tuned, personalized death machine. Most guns can be tweaked up or down the range scale with attachments. Something like the F2000 or AK-47 can be used at long range if you slap an ACOG on them, so that even a relatively inaccurate gun can be used for long distances when needed.
By comparison Halo 3 weapons can be broken down into rock, paper, or scissors based on their ranges. So, rather than focusing solely on grabbing weapons and engaging at prescribed ranges, a player’s goal is to position themselves tactically to engage from a point with favorable cover and ranges according to their class. Maps can be broken down into corridors, hiding places, and cover points to use while moving to various engagement points. All levels have multiple routes to any position, like High Rise’s tunnel or Afghan’s ambush cave. The point is this: you’re not running to pick up a gun anymore, you’re running to pick up a spot to shoot from. The map is very literally your weapon in Modern Warfare 2.
Part of the reason that I think describing Modern Warfare 2 as a remarkably map-reliant game is the way that the developers changed the formula of Call of Duty 4's approach to this kind of play. A great post by Matthew Gallant highlights the major tweaks to the game ("Refinement in Modern Warfare 2", The Quixotic Engineer, 23 December 2009). The irritating tactic of grenade spamming key attack points from Call of Duty 4 is gone. Players can only hold a limited amount while damage and range has been reduced. Secondary weapons allow a sniper to balance themselves out when moving from point to point. Whereas people would just carpet a point with grenades while out of sight in Call of Duty 4, in Modern Warfare 2 it’s a much weaker tactic unless you’re that asshole on Rust. Secondary payloads encourage people to not lock into one position and camp because they’ll be reasonably equipped while travelling. All of this is padded out with the improved MMO elements of leveling up and unlocking equipment, which encourages more complex play from players by using specific weapons and aiming for goals beyond "Kill Everything, and Die Less While Doing It". Even if a skilled player runs into someone that they clearly outclass, odds are that they’re fumbling around trying to get a bizarre kill or unlock a new ability. While not quite the same thing as "Race to the Weapon", it makes it so that players can engage with these complex situations voluntarily.
The difference between skilled and unskilled players has also been softened by giving each player a distinct sets of goals via kill streaks. If you’re just getting started at Modern Warfare 2, most of the low requirement kill streaks are beneficial to your teammates like the UAV or Supply Drop. You can still help even if you’re not bringing the kills. Copycat lets beginners steal a superior weapons layout if they’re getting torn apart and want to see how other people roll. One of the first weapons that you can equip is the lock-on rocket launcher, which lets a beginner chip in against Chopper-Gunner or Harrier attacks. On the other hand, a skilled player is going to be coordinating their killstreaks to build on each other until they hit the high level options like the AC-130. The point is that you can organize your class to be helpful if you’re bad at the game just as much as you can organize it around being a highly skilled player.
Maps in the game are organized around making sure that there is no one particular point that is strategically infallible. To the best of my knowledge, there are no positions where a player has access to multiple lanes of fire without having to leave their back unguarded. Snipers rely heavily on C-4 but can only plant two at a time, subsequent C-4 plants cause the first one to immediately explode. A pretty good video of someone both controlling a point and then retaking control of it is one by FJ509 showing a Level 19 player (albeit already prestige) on Scrapyard. At around 3:00 he’s moving through the bottom right corner next to the flaming propane tank. The fire & smoke makes it so that he can’t always guard his right side when facing the 818 plane (likewise for someone on the other side), but otherwise, he has a shot at every player trying to attack the warehouse from the right side.
Other moments like the choke off between the tail sections demonstrate the way that the map becomes a weapon: you’re moving into different corridors for firing. At 5:30 he makes it clear that the point at the lower right is strong because you can move between 2 corridors with decent cover either way. Other spots that are even better strategically, like the top of the office buildings in Highrise, are balanced by requiring you to make a tricky jump and leaving you exposed while traveling to them. That’s just two examples. Others would be Afghan’s cave, which makes you vulnerable to flashbangs, or Sub Base’s right-side office windows. Every position has a weakness. Pick a tactical point, methodically clear it out, occupy it for a few kills, notice when people are noticing you, and get out before they turn the tables. Hardcore mode does not seem to change all that much, but I don’t play it enough to be a valid judge. As far as I can tell, just hit pause if you want to see the map, shooting off someone’s pinky finger kills them instantly, and, aptly enough, the red-dot scope attachment replaces cross hairs.
While discussing the basics of learning to play in an e-mail Iroquis Pliskin summed the game up nicely, “Listen, for the first few hours playing the game you're just going to get your ass handed to you. There's no avoiding it. Map knowledge is too important. But you have to take it as a learning experience . . . Eventually you pick up on things and you get better.” The interesting question that such a map-heavy game like Modern Warfare 2 leaves me with is what happens once the majority of players know all the maps? Simon Ferari commented in an e-mail, “I have a rule where if I'm going to play a competitive shooter I've got to buy it on launch day and stop playing it after two months. At this point, the people who are still playing it every night will be so good that it ceases being fun for anyone who has to actually work for a living. If you buy the game a month after it comes out, you're not going to find copious amounts of other new players to learn with.”
While the game’s deep number of options and maps are still sort of being explored, eventually players are going to adopt a lowest common denominator strategy that everyone will rely on because it’s the easiest way to win. Prestige’s level reset is a good way to stem the tide, but I have my doubts about how many people are going to voluntarily go back to level one for a merit badge, which might be MW2’s biggest problem: it’s a game that always needs new maps to change up people’s play styles. Speaking purely as a mid-20’s gamer who can’t really put in the practice time to stay competitive, it might be the fastest I’ve ever seen an FPS game fill up with overly skilled players.