There's something to the vocoder engine that makes it unique and can produce all sorts of sounds. Destined primarily from my experience towards voice vocoding (from the labeling to the different options offered), this can also be a great morphing tool, when used right.
When I first got into experimenting with vocoders, I wasn't really happy with Ableton (or it's Grain Delay). It wasn't bad, but it just wasn't what I was after. Checking out Vocodex however left me very impressed! it's easy to think of FL Studio being filled with bloatware that you never touch, but Vocodex is a fantastic and deep vocoder!
Although I have NI Razor now and it can do incredible vocal effects, I'm definitely holding onto Vocodex :).
Vocodex allows some great control over your vocoding. It can seem complicated at first, but it isn't too hard to learn. The one bad thing is the way the band distribution is displayed, very unintuitive.
What can I say? Its a more-than fully featured vocoder with its own built in carrier tones. You need to experiment with the vowel filter and all these other wild features to really dig deep enough to enjoy this plugin! I really like putting this on vocal echoes to mud them up a bit as well as tune the carrier signal to match an interesting guide tone in the song I'm working on. Its subtle but it really is an interesting thing to do with ambience! Heck try it before a reverb plugin on a send, then add an expander to get the verb to pump with the drum groove.... but I digress. Super fun and super useful!