I tried this for the first time today, and I must say, I'm very impressed and I liked it.
I tried regular Vault a long time ago (a few years back) and when I drank Vault Zero, it tasted so familiar. It had a good Citrus flavor and I enjoyed it.
It also has a good caffine content, which is good if you're feeling down on energy.
I have 11 cans left and I'll definitely buy this again soon.