Darth Vader is number 1 on the list of helmets that Hasbro should make in their Black Series role-playing line. That is probably why they waited to do it forth, after the Kylo Ren helmet, Stormtrooper, and Poe Dameron X-Wing helmets they have already done. Once you do Vader, pretty much all that is left would be Boba Fett, which I am sure we will get. I personally have the Kylo and Stormtrooper ones. They both had their positives and negatives, but man does the Stormtrooper one display well on the shelf when not being worn. The Poe one is the most comfortable — when I tried it on at SDCC, I did not want to take it off.
It looks like all of the others in this line: stunning. Featuring full electronics inside the helmet, the back dome removes and shows off all the guts of the thing. That should also make it pretty easy to assemble on your head.
The sculpt on this thing is the seller here. They seem to have nailed the look of the helmet right down to the eyes. This is based on Vader's look from Return of the Jedi. The back connects by magnet to hold it in place, and features a sealing sound effect, as well as the iconic breathing effect. If it is like the others, it will also have voice-changing capabilities, as well.
If anything like the others, this will be available everywhere — but because it is Vader, I would expect it to not hang around on shelves for very long. The Darth Vader Black Series Role-Play Helmet should be on store shelves some time in the winter or spring. My advice? Preorder online and avoid trying to find this thing. It will probably be in line with the others and retail for around $90.