The new default for crtl+tab behavior in Visual Studio is to bring up a window prompting you with recent documents, allowing you to select a document and press enter to open it. I actually preferred the old way, where crtl+tab instantly opens the previous (next) document and holding crtl and pressing tab multiple times goes through the stack. Here's how to change back...
- Go to Tools > Options
- In the left nav choose Environment > Keyboard
- Search in 'Show commands containing:' for 'Window.NextDocumentWindow'
- Select 'Window.NextDocumentWindow' in the results
- Go to the 'Press shortcut keys:' and press crtl+tab
- Click 'Assign'
- Click 'OK'