I just tried both beta levels and the level designer, and although there are a few bugs and other issues, it was still a very enjoyable experience.
I liked:
The self-snapping tiles, it made things really easy.
The level design of the beta levels.
The copy/paste tool.
The ability to make moving blocks and planets with gravity.
Being able to change the default gravity.
The space-time control idea.
The ability to change whether or not the paths of blocks are visible.
And a lot of other stuff that makes a list too long to explain.
A few suggestions:
Make it possible to die from crushing.
Allow players to connect items to tiles. This would allow a whole lot more level design possibilities, such as a moving block with spikes on it (as an alternative, you could make a way to move linked items).
Allow someone to disable the space-time action (you may already be able to do this and I just haven't figured it out yet

).
Keep up the good work, this will be a very good game, maybe even better than SM63...