I just moved to BB10. Started webOS, then to Android, then to BB10.
Google Maps. I have it sideloaded but it's definitely much slower and less responsive than on Android. The BB Maps app sucks comparatively. I frequently find important streets unlabeled until I zoom in very close. Google Maps, I've almost never had this issue. The sideloaded version is ok though. I'm fine with it.
Google Talk/Hangouts and Facebook Messenger are available but inferior on BB10. But it's actually ok.
Multi Alarm Clock. Sure there's apps for it but the highest rated one I found had ads and required you to pay to enable multi alarms.
Feedly. Sure there's other RSS readers, but Feedly has my info and I find it much nicer than the RSS reader I downloaded off of the app store.
Duolingo. Was brushing up on German... Would really like to have it...
Glympse. I actually used this a lot. When you leave to meet up with someone, Glympse them. It was EXTREMELY useful and I'm really going to miss this app.
Google+. Not super important though.
GoPro. I have a GoPro. This App would be VERY useful.
LINE. Ok, so I can side load it, but it doesn't work exactly well. Has some weird behavior, but it's ok. "Use BBM!" Except I know exactly 0 people with BBM so LINE is a bit more useful.
Pocket. I have it slide loaded, but again not quite as smooth. But it's ok.
SpeedTest. there's speed test apps but none quite as good as the one by Ookla. But I have it sideloaded and it works ok.
Starbucks. Not really necessary but it's nice to check my balance and see if I have any freebies coming to me.
Yelp. I used to Yelp everything. No Yelp app. Sideloading won't work.
Yahoo Fantasy Sports. It's ok if it doesn't work though since I haven't cared too much about it.
That said, I'm actually liking BB10. The app selection is pretty terrible though.