Singleplayer - Short (~6hours, super fast-paced. Maps are extremely linear like usual. Veteran's not that hard, you just have less health and die very easy. The plot line is okay, but COD isn't really a game that excels in its storyline.
Multiplayer - Most people say it plays like MW2, which it does. Guns: Customization has been much improved - more attachments, new "proficiencies" (e.g. kick, damage, range). Unlocks go by weapon XP (which comes from kills AND challenges) till Level 31, which unlocks the Gold Cameo.
Explosives: The blast radius has been greatly reduced, so grenades are pretty ineffective. Noobtubes are nerfed, but still usable (but barely anyone uses them)
Killstreak setups: 1. Assault - streaks still stack, but it is MUCH harder to get high streaks. 2.Support - streaks remain after you die, so Stealth Bombers and EMPs become pretty annoying for most people, 3. Specialist - the perk bonuses are probably the most fun MOAB - 25 gun killstreak fun, only if you can get it. If you're used to high killstreaks in MW2, it's much harder in MW3.
Maps: are very small, and not sniper friendly. The DLC has a couple more sniper friendly maps. Host migrations: have been fixed, and don't take that long, which is a real improvement.
Theatre Mode: Allows you to continuously record gameplay (or turn it off), and upload up to 30s on free ELITE (to youtube or Facebook) (but uploading on ELITE has problems - the first couple seconds of a clip are always cut out, and many clips won't render at all) You also can't see the 1st person view of another player (only 3rd person)
GameModes - a couple new ones (Kill Confirmed), and community playlist, which are updated, so a new mode regularly appears (e.g. Drop Zone, All- or-Nothing, etc.) There's no Combat training, no ballistic knives, crossbows or dogs, like Black Ops. I wish they brought those back.
Faults: Grenades are hard to use. Some overpowered deathstreaks (Dead man's Hands). Some OP weapons (Akimbo FMG9s) but continuously patched (like the Striker). Overpowered Support Streaks (Stealth Bombers and EMPs). No Commando, but knifing is not as good as MW2.
Spec Ops Survival: Survival mode is pretty fun- troops, helis, and Jugs. You can only play alone or with a friend, (not 4 people like Black Ops, but I guess the small maps are the problem). The survival maps are the MP maps so there's no unlocking rooms. The weapons are the same as MP, but guns, especially snipers respond slightly differently than MP. And as a warning, some people get bored pretty fast with Survival.
Spec Ops Missions: 48 stars to complete, much easier than MW2, but the long ones are annoying if you die halfway and have to restart.
ELITE: Get it if you plan on getting all the DLCs, otherwise, you could buy another game with that money. If you don't buy it, you can still have most of the free ELITE benefits.
OVERALL: SPs fun but short. Survival is fun, but can get boring fast. SpecOps are the usual. MPs good, but has its faults. It's better than MW2, but don't keep your expectations too high. Many of the MW2 problems have been fixed, but there are still many problems. Try not to get frustrated with its faults, and have fun (I know, sounds stupid) otherwise, you might hate the game. Plus, if you don't play online, get another game, since Multiplayer's the main focus of MW3.
