Having used both Aperture and iPhoto extensively since 2008, I feel that Photos really does slot in pretty much between Aperture and iPhoto, and once 3rd parties begin to produce Extensions, a lot of what may have originally been lacking could be reintroduced. It's a brilliant model actually - Apple creates the shell of the app, which covers organization, important controls and features, and sharing FOR FREE, then 3rd parties can create additional functionality that can be sold on as as-needed basis. Want to brush in adjustments? Buy an extension. Want to do more to your metadata and GPS location? Buy an extension. You can make your version of Photos as streamlined or complex as you need it to be.
A lot of the editing controls are hidden by default, and it requires you to use folders and Albums structure differently if you liked to compartmentalize your shoots by events. However, I have found that the Moments works well enough that I rarely need to create additional albums. The thing I miss most from Aperture is the ability to brush adjustments in, or apply adjustments to just midtones, highlights, etc.
A feature that I thought I would get in use out of but can now say otherwise is iCloud shared Albums. My family and I went to Comicon this past weekend armed with 4 iPhones, a Nikon DSLR and a Fuji mirrorless. After such an event, we typically email our best shots around to each other as some like them for their social media, others for albums/projects, others to print. It's a mess sharing all these shots with this many cameras. For this event we used the shared Album functionality. The iPhoneographers made their edits on their iPhones or iPads, and my son and I added our shots to Photos on our respective Macs and made our edits there. When we were all finished, we all just dragged out best shots into a Comicon iCloud shared album, and these were instantly available to everyone on all of their respective devices. No sharing of iCloud accounts, no sharing of libraries, no emailing images or putting them on memory sticks - they just showed up. I can see using this quite a bit.
