Oh and spartan, this should help you quite a bit :D
Killzone 2 Ranks:
Rank: Private
Points: 0
Unlocks: N/A
Rank: Corporal
Points: 30
Unlocks: Squad creation
Rank: Sergeant
Points: 100
Unlocks: Clan creation
Rank: Sergeant First Class
Points: 200
Unlocks: Shotgun, SMG
Rank: Master Sergeant
Points: 350
Unlocks: Medic Badge
Rank: Sergeant Major
Points: 550
Unlocks: Light machine gun (Helghast, Vektan)
Rank: Lieutenant
Points: 800
Unlocks: Engineer Badge
Rank: Captain
Points: 1100
Unlocks: Missile Launcher
Rank: Major
Points: 1450
Unlocks: Tactician Badge
Rank: Lieutenant Colonel
Points: 1850
Unlocks: Assault Badge, Grenade Launcher
Rank: Colonel
Points: 2300
Unlocks: Saboteur Badge
Rank: General
Points: 2800
Unlocks: Scout Badge, Sniper Rifle
When you level up, start unlocking things, you'll find yourself getting much better. I got General earlier today after 14 hours of online. Now i primarily snipe (its freaking insane, invisibility is so full of win) and though i may only get 10-20 kills in an entire long match I will only die 1-5 times, usually around the 1-3 mark.
Oh and the biggest differences in your skill will be first when you get the shotgun, and when you unlock the assault class, mainly because the combination of A.) The Extra Armor B.) The Boost Pill and C.) The Grenade Launcher will make you a force to be reckoned with. You can run directly into an enemies base with the boost skill in effect with the assault class and nade people with the grenade launcher, get anywhere from 2 to 10 kills before they pick you off lol :D its insanely amazing. Doesn't always work though, but when it does... it will be a moment to cherish.