How does the security features differ from standard android phones? Is the only difference the apps that can be just as well installed on a standard android phone in the play store or are there some additional layers?
Well, it depends on what you mean by "standard Android". There are some non-exclusive features and some special.
BlackBerry provides monthly security updates. This is not exclusive, for example Google and Nokia provide security updates, too. Some other vendors provide regular updates for a subset of their portfolio. Maybe some of them are even faster than BlackBerry. But BlackBerry phones are still much better than average there, because many vendors completely ignore security updates.
BlackBerry also provides state-of-the-art security features like verified boot, downgrade prevention, encrypted filesystem and so on. I am not sure about others in the industry, but at least, BlackBerry is likely not worse than others. I believe that some of those are now requirements and some are done voluntarily, so I guess BlackBerry is slightly above average there.
BlackBerry has also some visible exclusive feature: DTEK. Please don't confuse DTEK app with DTEK phones, BlackBerry makes some mess in naming. DTEK is some security suite that contains not only a security checklist (that might advise you, for example, to require PIN for boot), but also allows you to manage permissions of all the apps (and revoke them even for pre-Marshmallow apps) and watch their usage (e.g., find apps frequently accessing location in background, or even be notified when some app accesses location in background). Of course, this is not just for location, one might be also concerned about other permissions.
AFAIR, BlackBerry has performed some kernel hardening, but I don't remember details.
Overall, BlackBerry seems to be a reasonable choice if you want a reasonably secure Android phone. It is not the only reasonable choice, as there are some other choices that might be good, too.