tl;dr: ~600 GB photo library, took ~3 weeks to migrate, some things are awesome (access to all my photos everywhere, on any device), some things less so (faces don't get synced, no loupe, no five-star rating system, no pro-level editing/batch workflows). All-in-all, I wish Apple didn't ditch Aperture... but it's not the end of the world moving to Photos.
There are many, many photographers who were disappointed Apple decided to discontinue Aperture development. Aperture was by far my favorite tool for both organizing and manipulating RAW photos taken with my DSLRs. It was fast, it had tons of great organizational features, and was highly adaptable.