I'm an unabashed Sparkaholic. I'm sorry if you clicked on this link looking for a critical, nuanced preview of Microsoft's new game that makes games, because I'm the wrong guy for that. I'm in love. Project Spark comes out during the "launch window" of the Xbox One, will also ship on Xbox 360 and Windows 8, is free-to-play (with copious amounts of paid DLC likely incoming), and it's everything I ever wanted.
What I love is the editor
Project Spark gives you a number of ways to create games. The easiest option is a choose-your-own-adventure-style editor, where you choose a world type, a character type, a mission type, and then get tossed into the dynamically-generated world and begin playing. After you complete that chapter, another set of choices is presented, and so on until you've played and "created" an entire game. You can share that game with others, or edit it yourself to make it entirely different.
The default Spark gametype is something like a Zelda or Fable-style action game, but if you want to get your hands dirty, everything is entirely customizable — you could create a 2D platformer, or a 3rd person shooter, or a tower defense game, or anything in between.
For me, however, I doubt I'll spend much time playing games in Spark, and especially none of the pre-built ones. What I love is the editor.
When you create a blank world, you're presented with a vast, shiny plane. It's not massive, but it's large enough to make a Zelda-sized level, and you'll probably spend too much time fiddling with the details to worry about where the edges are. The editor is essentially a 3D modeling program, with tools to extrude and mold the landscape, paint it with an intelligent biome brush, and place objects to your heart's delight. While all of this is possible with an Xbox controller after you get used to the button assignments, I surprisingly preferred the SmartGlass tablet interface.
Project Spark actual gives you three ways to control it: the Xbox One controller, SmartGlass, or a keyboard and mouse. Additionally, Kinect voice integration might be included in the future. These can even be used simultaneously: you could design a game where one person controls a character, while another person clicks on stuff and mashes the keyboard. What's astonishing is that it all actually works. SmartGlass mirrors the Xbox One's display, but when you start manipulating the editor with your tablet, the UI changes for touch-friendly controls. Camera control and object modeling is totally intuitive and surprisingly powerful with multitouch, and menus are always best navigated by tapping.
Then I made my playable character a tree
But modeling your world is only the beginning. Project Spark lets you bring it to life, with deep AI options assignable to any object in the game. You can give a stationary rock physics so it rolls off a cliff, or teach it to follow you, or just play the game from the perspective of a rock. Spark includes pre-built AIs for many character and object types — aggressive ogre, exploding bird, and the like. That AI can be edited in ways so deep and fascinating that I can't imagine myself doing anything else but assign absurd, emergent behaviors to everything in sight.
When I finally got a chance to play the game, I knew exactly what I wanted to do. I had no idea how, and I did it anyway. I dropped an ogre into my sparsely decorated world, then gave it "bird" AI so that it would fly away when I approached it. Then I told it to follow me when it flew. Then I told it to follow me, pick me up when it found me, and fly me into the sky. All of this worked. Then I made my playable character a tree, walked over to the ogre, and was instantly nabbed and lifted aloft once more.
I only scratched the surface, really. Your character can deform terrain and paint with a biome brush in-game if you assign the appropriate behaviors. You could create any sort of mission type you can imagine. The AI editor has deep nesting and allows for multiple "pages" of behaviors that an object can switch between. I don't even think I can keep listing ways to use this game, I just want to run back to the booth and play it some more.
What game have you been dreaming of? Project Spark just might be able to build it. Or at least help you make a really smart rock.