Difference between MULTIPLAYER Resistance and COD4 on PS3?

The Call of Duty series (made by Infinity Ward, so 1,2 & 4) all has great online. I have 2 and 4, 2 on PC and 4 on PS3. Modern Warfare is very very very good online, it takes a while to find a game sometimes, but its really deep and very well done. You get to level up, unlock new weapons, and cles (things like extra ammo, more bullet , 3 primary weapons). So don't hesitate to get it, Its well worth 60 bucks, you'll be playing it for years, trust me.