How is the gameplay in the retail version different?
Place a ghost brick, number pad moves it around and places bricks, you can jump, you can move, you still have jets but now your feet have jet particles coming from them, you can still customize your player, but in more ways than what RTB 1 allows, it's got a bunch of weapons, items, and tools (counting the community made stuff)
The only downside is not having an Editor Wand, which is an acceptable sacrifice for everything else the game is capable of