BF3 is awesome! COD is child's play in comparison.
Its hard at first but the more you play it the easier it will get (better guns and know the maps)
Its pretty tactical... best when you have 4 of your mates in your squad and you all have head sets.... I've found it best If 2 of you be a medic to revive each other and the other 2 be assault to replenish ammo!
You also have "perks" which you can level up to "squad perks" (so your whole squad benefit your perk) If all 4 of you pick different perks makes you a stronger team!!!
Have fun!!