Drupal - Cannot edit my views.. I get a JSON string?

Based on @Clive's suggestion in the comments, I found this issue:
JQuery Update breaks Views UI

So Views UI is not compatible with jQuery 1.8, and the OP has already confirmed that this was the problem.

This problem isn't limited to Views though. Other contrib modules depend on the default core version of jQuery (including Rules). An issue exists in the jQuery Update queue to Allow different version for administrative pages. And a patch was applied to dev on 20 MAR 2013.

The dev version of jQuery Update provides a update to the Configuration Form that allows you to select a different version of jQuery on administrative pages.

Before

After

I can confirm that setting the "Alternate jQuery version for administrative pages" select list to "1.5" after upgrading to the dev version of jQuery Update fixes the issue with Views.

I have had this problem before, usually on reallly big queries too big for the default mysql sql packet size. Rather than mucking with that -- try turning off Javascript/AJAX in the Views in the views administration settings.

It's not as neat without ajax views admin pages -- but this usually fixes it.

EDIT:

Login as administrator goto /admin/structure/views/settings/advanced and check Disable JavaScript with Views. Then Save that configuration page.