This level, called Tech Gone Bad, was built using Doom Builder 2 and was designed as a coop or deathmatch level. You're faced with a lot of carnage as you're sealed into an installation behind a steel door. Now you, and maybe someone else, have to go find that portal and stop those demons from continually coming through and ruining your day. So far it's been well received by the community, as it should be from the creator!
It seems that DOOM is a game that'll never truly fade away into oblivion, like some older tend to do. Instead it's kept very much alive by the community who love the classic look and feel. It doesn't hurt that it's a fantastic game to actually play too. And now John Romero himself is back at it. And this is only a warm-up for him, so we can expect more in the future.