Black Ops
It has a much better way of unlocking stuff. Instead of leveling up and just unlocking guns and then use them to unlock all the attachments and stuff you can use an in-game currency to buy attachments , perks , equipment and other stuff.
You still have to reach a certain level to unlock a weapon so you can buy it with the currency but once you "buy" a weapon you could just go ahead and buy the attachments and camos instead of having to play with an inferior weapon that has no attachments at all.
The in-game currency does not cost any money - you just have to play matches / level up or do assignments to get some "COD-points". You can also make your own personal emblem and put it on your weapon.
Overall the customization is much better than in MW3 - in MW3 you can just get a preset amount of titles and emblems by unlocking them and there are only a few gun camos while in BO you can just make your own emblem , put it on your gun and select a gun camo just buy it for a few COD points.
The appearance of your character / class also changes depending on what primary perk you have selected for that class. You can even change the color and shape of your red dot.
There are a few weapon balance problems here and there *cough* AKS74U&Famas *cough* but you can get these weapons rather early anyways and overall it is pretty balanced. The same goes for the perks ( which you can ALL unlock immediately once you get the class editor ) The balancing however is MUCH better than in MW3 for example.
Finally the killstreaks in Black ops are more balanced and don't stack - meaning that getting a kill with a killstreak won't count for the next killstreak which is a much better and legit way to get a powerful killstreak. Oh and Zombie mode of course.
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