I use Whatsapp, Riot (APK from Google Play with GCM enabled), Google Maps, and a bunch of other apps that depend on Maps and GCM services and all of them work fine.
Sometimes I almost forget I don't have GoogleApps installed.
I'm trying to figure out how to rebuild from non-official github repos, then I'll look at setting up a proper automated build of my own.
Works fine for me. I only use Google services to play Ingress and Pokemon GO, and both work without issue with microG.
OpenGApps are just the usual bloated proprietary Google Apps, just packaged in a nice and handy way.
But anyway, what's the point if I'm going to use ~10 of proprietary GApps anyway (maps, keep, inbox...) ?