Wow, dreams is something very special in my estimation. Also, I'm in the beta/early access, so the release might not seem like this huge event, but it totally is for me. Dreams is mostly a creation suit and community, but with the release comes:
1) The story mode: 3 different adventures in one story, with 3 different playstyles: noire point & click, sci-fi 3D platformer, fluffy dr. Zeus co-op adventure. It is going to be something really different and special. Very much looking forward to it.
2) Multiplayer - this is in playing and creating. Having a creation-session with a friend in LBP was so jolly and with dreams, this is going to be on the next level. Imagine tinkering on gameplay loops and writing a story togerher with a friend. Thats really my jam.
3) VR - this is the biggest thing for me, since vr-content is a bit sparse right now (I'm currently playing astro bot, but I'm saying that and everything else has been out for a while now). Being so immersed, alking around in a world of your own creation, that must be just breathtaking.
4) Way more players getting into it and I would assume Media Molecule releasing content (levels, music, charakters, artwork, tutorials, etc.) on a steady stream means that everything is gonna get bigger and better. More assets to choose from, more inspiration, more people to work with on your projects.
In a year with FF7 remake, TLoU part II, RE3, Ghost of Tsushima, etc. this might be my most anticipated and moat played game, when everything is said and done.