Are you familiar with Little Big Planet at all? Media Molecule has said everything from that will be in this, and a whole lot more:
As for the campaign itself, you can bet on Media Molecule mainstays like platforming and puzzle-solving, but that's just the start. "You can make amazing first-person shooter levels if that's what you want to do," explained Evans. We've already seen racing and flying games in sizzle reels, and the team is dreaming of the "new game genres" that could be created within Dreams.
All of the "electronics" (Media Molecule's name for the instructions that make games move and react to input) developed for the LittleBigPlanet series are there; they're just refined and improved upon. The team is trying to make it simpler for inexperienced creators to get involved by letting them use both its and other users' creations. You'll be able to, for example, search for "door with hidden lock," and then insert and remix it in your game, rather than creating it from scratch.
I think one of the key things that makes Dreams exciting is that players that are great artists can make content, like wooden bridge that falls apart as you run across it, and then other players can pick that up and drop it in their level to use. We're going to get some crazy awesome stuff.
But lest you think, "that all sounds nice, but show me how that plays out", take a look at what people can do with LBP3 already. Then imagine the ability for people take remix each others stuff with the advanced tools of Dreams:
LittleBigPlanet: The Sackies 2015 - Logic Creator