Coke Zero for the US market still uses aspartame, the same sweetener used in Diet Coke.
Coke Zero is a more modern formulation which is supposed to taste more like "classic" Coke than Diet, which has its own distinctive "artificial" flavor which some customers have become accustomed to. It's also marketed very squarely towards young men: during the recent "Share a Coke with X" campaign, there was even a "Share a Coke Zero with a BRO" can, which made me laugh a bit.
Coke Zero is a more modern formulation which is supposed to taste more like "classic" Coke than Diet, which has its own distinctive "artificial" flavor which some customers have become accustomed to. It's also marketed very squarely towards young men: during the recent "Share a Coke with X" campaign, there was even a "Share a Coke Zero with a BRO" can, which made me laugh a bit.