Has potential, but could use some serious improvements,
Sandbox is... yeah. The usual issues arise here. All of the 'spatial relations' benefits come at the cost of usability. Anything you do to increase usability flattens or otherwise breaks those relations (see exiting the MC's room dumping you into the main hallway instead of outside the room - more usable, but ruins the sense of where the room is). Once there is more than one option, you also get the other usual problems - searching the entire map to avoid missing things constantly, and continuity errors due to the sheer number of orderings. But apparently some people like it, so... maybe this one is more personal taste.
More objectively, the transitions. They are pretty painful. So much variation. Some don't skip, some skip a lot, some skip normally. Same for rollback. It would be great if they behaved normally. Don't tie them together, or block skipping, etc. I realize the animations probably have to break this a bit, but it's worse than it needs to be.
I'm also worried by the sheer number of apparently big choices already. This doesn't seem manageable. The things combine combinatorially, so... yeah. That's way too many routes, never mind the number of scenes.
I do like the idea overall. There also some other nice decisions, such as not using a decreasing power pool in the use of flags instead of slow buildups of points via grinding. But there are some things that could be improved, and some that might case problems in the future.