Doom Snapmap demonstration:
https://www.twitch.tv/bethesda/v/62765871
(starts at 12:50)
Single player preview:
https://www.twitch.tv/bethesda/v/63182030
(starts at 0:40)
I don't know how many spoilers there are in the SP video as I haven't seen it yet.
As for the SnapMap video, it starts off with a custom 4-player deathmatch game with sped up player movement, shotgun only spawn and weapon pickups in the level... you know... exactly how the Doom multiplayer should've been out of the box, god damnit.
Other points of interest in SnapMap:
- They showed a custom coop map where you have to pick up powercubes dropped by monsters and return them to a safe zone. Returned powercubes extend a timer that's running down. The monsters spawn in greater numbers and are easier to kill so you can keep picking up powercubes.
- Third map they showed was "BasketBoom", which is a basketball-ish type of game without weapons. You can pick up the ball and try to throw it in the hoop as if it were a grenade. If you don't have the ball, you can melee punch other players to steal the ball.
- Fourth map was a SP experience with lots of level interactivity (bridges being activated, forcefields getting activated blocking your way until all monsters in the room are killed, a door locked by a red keycard).
- Tower Defense maps, Parkour maps (think Defrag, but really boring due to the dumbed down movement) and wave challenge maps (think Gears of War's Horde mode) are possible.
- They did show a map where you simply stand in a square room with a box in there and it says "shoot the box when the counter hits 10" or something. It then starts to count: 1... 2... 3... but then it stops counting. You have to continue counting up to 10 seconds in your head and then shoot the box when the counter should hit 10. Then it tells you by how much you were too early or late.
- They also showed a map where you had to enter a room, memorize something about the room, move into another room with two doors and it'd say something about the room. Then you'd have to enter the left door if the statement was true or the right door if it was false. If you enter the correct door, you score points. Rinse and repeat.
- They showed a map with (I think) a Mancubus that was totally ramped up with health and had had all sorts of special abilities like spawning other monsters into the room, temporarily teleporting you to a different place (some kind of hellish area with some kind of motion blur screen effect and flames in the background) and slowing your movement.
- The craziest thing they showed was a map that was basically a fully functional piano with drum sequencer in there.
- You can let SnapMap do a lot of stuff automatically, like adding props (think crates and stuff), clutter on the floor, decals and even enemies, but you can also place all that stuff by hand.
- You can do in-game cinematics with a camera system.
- You can add sounds/voiceover effects.
- Branching: you can take someone's custom map and modify it yourself
- Leaderboards: each custom maps has a global leaderboard
- Coop mode is possible in various forms. Four player coop or even in teams where both teams have their own objectives or you can have players play as demons.
- Every object has a number of events (like a weapon has an onPickUp event and a monster has an onSpawn or onDeath event). These events can be selected from a radial menu. Then you pull a line from the object to another object and it'll show a radial menu with possible event handers (for monsters like spawn the monster or for objects like remove the object, etc).
- You can customize the amount of damage weapons do, how much health players or enemies have, that sort of stats stuff, including scoring mechanisms. So yeah, you can bump up the damage of that weak ass rocket launcher
- You can determine what items enemies drop
- You can show text notifications center-printed in the screen
- You can put live scoreboards into your maps
- Player inputs can have different effects. The BasketBoom maps had the fire button wired up to be a sprint boost so you temporarily run faster.
- On release, there will be a large number of SnapMap maps made by id Software.
- You can vote maps up or down to rate them.
- SnapPoints: You earn them for both creating and playing maps. You can use SnapPoints to buy vanity items.
- SnapMap maps are cross-platform
- Bethesda is planning on organizing MapJams or whatever they're going to call it. Make a map that has to abide a set of rules, tag it with a specific hashtag (you can add tags to your maps for easier searching) and maybe they'll even pick a winner.
- If you have just 5 minutes, open the SnapMap video, skip ahead to 1:12 and you'll see a really intense fight that gives me the confidence that you can recreate the hectic battles of the Doom of yore in this game.
- In short, it looks like you can do some cool things with SnapMap
Must look into that 
GTX 680 (GK104) did.
