Resistance 2 Forum

I just got a PS3 and one of the games I got was Resistance 2 since that and Killzone 2 (the games I was looking at for online shooters) seemed to be mostly £40 but I saw Resistance 2 for £20, 2 for £30 so I choose that. But I havent managed to play into the multiplayer so I was wondering whether purchasing the pack pack in neccasery for online play in terms of how many matches I can get into, whether I will keep getting kicked when a new map comes up etc.

Thanks for any help you can give.