Just no. This is LBP taken to the next level.

What I want to know is how much you can customize the way a character moves and how the game feels to play. Like is there only a limited subset of mechanics you can have for a platformer? Or could I if I wanted make it play like Sonic or Mario with some fine tune logic editing?

Do you want to be frightened?

https://www.youtube.com/watch?v=9ihLm7bDkLk

Lol the momentum keeps building up for Sony, it seens everything they produce inhouse is a masterpiece these days. Dreams is not my kind of game tough, but depending on how good it is I might give it a try.

That's all good stuff, but could I for example develop my own gameplay mechanics? Or is it like LBP with only really one way to play, as in crappy floaty platforming? Will the games you can make actually be good?

Yes, you can recreate any gameplay mechanic from any of your favourite franchises. This is just the easy stuff. If it's floaty then it's because the creator decided to make it floaty. 

Then that's amazing.

It's difficult to explain to people what Dreams actually is. With LBP, most of the assets and animations were created outside of the game and then imported into the game. Dreams is a development tool, just like Unreal or Unity. Every single aspect of any games made with Dreams is down to the creator. There ARE set things for beginners but you can go much deeper if you wish, OR you can simply borrow what others have created and adjust those accordingly. 

Another preview:

https://venturebeat.com/2018/05/21/dreams-shows-the-ps4-is-ready-for-littlebigplanets-evolution/

Dreams, as the name suggests, is a game that is full of possibilities, and many questions. After seeing what was possible in the game I am more excited than ever to finally get my hands on it, but I also question what depth of game will ship when you first boot up the experience. I love the concept, and after playing 45 minutes I want to play more, but not everyone will want to build, some may just want to play. I just hope that Media Molecule has learned from Little Big Planet, and supply a robust game within their toolset. Relying on a community to fill out content has the potential to backfire on the studio if not done right, as many other titles have proven in the past. Having said that, Dreams is an impressive achievement, one that pushes what is possible in gaming. While it may not be for everyone, if Media Molecule can deliver on the potential of this demo, Dreams could be a major step forward in gaming, and one of the releases I am most excited to see hit the show floor at E3 2018.

https://www.cgmagonline.com/2018/05/21/dreams-hands-on-preview-a-world-of-possibilities/

Yeah I see. Also this thing isn't just a game maker but a 'whatever-you-want maker'. Wether that be an animated movie with voice acting and your own composed music, or even just a piece of static art. I also saw the music stream where that one guy made a DJ machine in play mode (seperate to the music composing tool), that's like beyond Minecraft levels of creation. It's micromanagement of unimaginable levels. God knows what people will come up with. You can make NES emulators in Minecraft, maybe you could in Dreams? Or even PS1 emulators? lol.