Having the same issue as described by OP. Logged off to see if I can change the text size through the launcher, and now I can't even get the launcher to start. MS Store goes from checking files, calculating download size, almost ready, then back to downloading. I'm trying the "Repair" feature that Daigoji mentioned, however it has been "repairing" with the circles moving for almost an hour now.
Like many, I have been excited for this release, and actually updated from Windows 8.1 to Windows 10 just so I could play this game. Hopefully they can fix it soon.
Sorry you're having these issues. I just exited game myself and dreading having a restart issue after dinner.
Quick question, when you updated to Win10 how recent was it? Did you fully download and install all the required updated drivers for your devices, mobo, etc. Also have you run Windows 10 Update a few times? Just want to rule out it isn't a Win10 update issue.