get Game Fly and rent both.
I have played both and Enjoy RB6v2 better,here is why:
what COD4 over RB6v2
Perks! (more ammo, more stopping power, Last stand. etc)
Kill Bonus (ie air support)
Fast pace action (meaning there is alot of RAMBO action or One man hero stuff)
What RB6v2 has ov COD4
Wepon feature and modes (fire modes and a hand full of add ons per gun. Modes like Single, burst or auto shot. Features like scopes, laser sites, recoil reducing stocks and larger ammo clips)
Character customization Female and Male. (add your own FACE to ur avatar. Change headgear, shirts, pants and accesories like masks and glasses. Change ur armor with Actual effect. Meaning if u have no armour on ur legs hits will hurt more there! you can also Change the color of ur apearal, you could be all black like a shadow or as bright as hot pink)
COVER. (you can take cover behind walls and depending our ur gear u can be completey hidden or if u have alot of armor or a long Sniper rifle some of it may be slightly exposed.)
MORE demo and special wepons (breach charges, C4, Smoke, tear gas, gps, motion sensors,flash, radar jammers, frags, incineraries, etc)
now beside the stated highlights both games are fairly different.
COD like ALL CoD games has a more acade like feel. Easy to pick up meaning easy to master. this also means everyone is on the same simple learnign curve. This being said team work is not nessicarily needed. One man can take out several given the right but fairly common situation in a matter of seconds with basic efforts. Not saying CoD games take no skill. its just a differnet kind of skill.
RB games like ALL RB games have been souly on teamwork and realism. Shots Hurt ALOT and recoil is stupid real. This being said, One man army is nearly impossible and team work is almost required.
I mainly enjoy RB6 over CoD because Im forced to use TEAM work. if I was just running around gunning down my enemies then whats the point of playing Online? its not much different then play against AI.... RB6 Truely brings out the online gaming experience
I not rating the game on single player because that involves a story and liking or disliking it is a very personal question which only you can answer.
and to be Fair. Rb6v2 is newer and Im sure the devs took some Key features from Cod4