To headshot someone through a box or wall they are trying to hide behind. I really like the way bullets pass through some cover, it's obviously nothing new (even the first CS had this) but its still pretty classy when you kill someone that way.

I like the minor class system too. For example, grenadiers (I believe?) get a last stand option. Ghost are quieter than others etc.

I heard there was a hit detection bug on the online multiplayer for PC on the sniper classes. Wondered if thats the case for Xbox?