You've the option to re-download Apple's in-house apps for a while, but you haven't been allowed to write App Store reviews for them like you can for third-party titles. Apple is now treating its apps more as equals, though. 9to5Mac notes Apple has quietly enabled App Store ratings and reviews for its own software. If you want to laud improvements to Maps or trash Mail, you can.
The volume of reviews is relatively low compared to equivalent third-party apps that have been around for years, like Gmail or Google Maps. However, it won't surprise you to hear the ratings are relatively low. Apple's Podcasts client is sitting at two stars as of this writing, while Apple News is sitting at 2.3 stars. Maps has only partly mended its early reputation with a three-star rating. Like with third-party software, some customers are using the ratings and reviews to gripe about technical issues instead of design.
The change treats Apple's apps more fairly, and might even be useful to help the company spot and respond to criticism. It might likewise see this as another way to improve public perception of the App Store. On top of an Epic lawsuit that could soon force Apple to alter App Store policies, the iPhone maker has preemptively stopped favoring its own apps in rankings and reduced its cut of small developers' apps revenues. Ratings and reviews won't dramatically change Apple's image, but they likely won't hurt.