Google Home launched with a number of missing features, some of which have been addressed. Not all of them, though. You still can't set a reminder, but you can finally tell Home to play songs that you've purchased or uploaded to Play Music. The preference it gives to that content will vary based on your account status.
Previously, Assistant on Google Home would only play songs from Google's online catalog. So, anything you uploaded or purchased on Play Music would not be included. That was severely limiting for anyone using a free account. This change makes Home much more robust for Play Music users. If you have a free account, your uploaded and purchased content will be given preference over free radio streams when you tell Home to play something. For paid users, the on-demand catalog will get priority. If you request something Google doesn't have, it'll go to your personal library.
There are a few caveats. Commands to play music based on genre or activity are still limited to the on-demand catalog. Also, personal playlists will be prioritized above your default music player, if that's not Play Music. To access Google's on-demand catalog (free or paid) in that instance, you need to add "on Google Play Music" to your commands.
This update is currently rolling out to everyone, but Google didn't offer a timeline.
- Google Product Forums