Hi, welcome to the world of Windows Phone aka. Windows 10 mobile, first of all. As an android user previously, I will say that you will find the app gap annoying for sure initially, if you've read or watched reviews elsewhere they'll tell you the same. This has been a problem for the platform ever since Windows Phone 7 was released in 2015, luckily for some of us early windows phone adapters, since we started using the platform so long ago we're used to this by now, and I can tell you that even though in my friend circle I'm considered an extreme app *****, I get by perfectly with all the apps that's available on WP, both for daily apps and entertainment purposes. Yes, I do enjoy the amount of apps when I use my android tablet and when I briefly switched to Android this past summer when I went back to Taiwan, but as a phone OS I love Windows and will not very likely switch to Android or iOS (I explain a little bit below).
Here's the good news, if you haven't read. MS is doing their best (at least they say they are) to encourage developers and port apps to Windows 10. Project Astoria is for Android apps (which is currently on hold for technical and other reasons), and project Islandwood is for iOS app and is still in the runs so we should see apps coming aboard soon (a few already done like Candy Crush and in the works like Facebook, Messenger).
One major thing I like about Windows mobile more than Android include the update experience, updating the OS on Android is a mess, with compatibility issues and support for different devices is terrible, some older devices only get 1 or 2 OS update and then that's it no more. Also, both my android tablet and phone is buttery smooth at the beginning, but after few months they just become laggy and buggy, no matter what I did. Windows Phone has never done that for me. It is ALWAYS smooth. Not bug free, but overall a much more pleasant experience.
What about iOS? Yes it runs super smooth and seemingly bugs free, but it's just dull and too plain. And anyone with a pair of eyes should be able to see Apple's decline since Jobs left, I mean even die hard Apple fans told me that.
Anyways, I hope this helped, you can read more about
Project Astoria/Islandwood here. And enjoy your L 950XL! I'm still patiently waiting for mine, still rocking the Lumia 920 from exactly 3 years ago.