Hello,
The standard create link interface has been replaced with a custom one for better integration with BC. While in the redactor you could manually enter a URL and define a target (actually only specify to open in new tab), the custom interface on BC allows you to browse for selected bc resources, which makes far easier to add internal links. As for setting a target, we're aware of the miss and it will likely be added anytime soon.
One additional note, while the editor is based on redactor, you should not expect the 1:1 match in features as we have replaced some of the controls for better integration and support of BC features. Some examples are the link manager, the image manager, the code view. We've also added additional features like CSS selector, which is missing in the standard redactor implementation.
Regards,
Cristinel