Bethesda very recently tweeted that, per the terms of the non-disclosure agreement, people taking part in the upcoming Doom multiplayer alpha "cannot share content" taken from the game. But it's also thrown up a closed alpha gameplay trailer on YouTube, so even if you're not playing, you can get a good feel for what's going on.
The video opens with Doom Executive Producer Marty Stratton delivering the usual caveats: It's an alpha, it's early, it's not a "game demo," and it's not representative of the final product, etc and so on. Be that as it may, Doom looks very promising, and there's a little bit of everything on display: A variety of weapons, a spot of melee, some powerups, and even a moment of demonic transformation.
The first Doom multiplayer alpha test kicks off at 12:01 am ET on October 23 and runs through the weekend, ending at 11:59 pm ET on October 25. The alpha is closed and signups are limited to those who are eligible to take part in the beta, which will happen at some point down the road. If that's you, and you haven't already put your name in the hat, you may do so at doom.com.