I agree that on Launch there were a lot of key apps missing and that was clearly BB/RIM's fault - they should have done more before launch. But currently all apps are available, and you can install almost all Android apps anyway if you have an app fetish.
Really, I use maybe 20 apps and not more than 5-6 ones regularly. Though i admit i do have around 80 installed ! Just in case I need them someday. As regards what is so awesome about BB - you don't know what you are missing. It's like asking someone to write done the advantages of a certain good vintage wine over one of the cheap ones !
Let me just say that I am a gadget freak and pretty much have a whole arsenal of Apple/Samsung/Nexus devices and even a Nokia Lumia. But every time I try to use any one of them I just can't get over the lack of gestures. My thumb just swipes up to wake up any device before realizing I need to push a button.
Then I miss swiping to peek at the message Hub to see all my messages in one place which you can peek without going out of the app you are using. I miss the flawless UI performance which never freezes even for a micro second. You can swipe through 8 pages of app icons in a quarter second and you will see all of them fly by. Do that on Android or iOS and you see the minute difference. And this is when there is actually No way to move through the pages so quickly in ios/android. you have to move one page by one page.
Then let's look at security. Which OS has never been rooted or jailbroken. Ever. Only 1 answer. BB10. (Previous BBs had a workaround of loading a really OS version and then running the various hacktools to get access to some things. Not in BB10 inspite of all efforts.) I am still trying to at least get to Root the Android Runtime in BB10 but no progress or hope yet. You can load the worst of the apps but it never ever crashes the OS. you swipe up diagonally and it goes into its own small window which you can kill.
That reminds me, switching between apps - running apps, not frozen ones like iOS or just screenshots of last few apps in Android - is very nifty in BB10. In iOS 7 I understand it is almost similar. The overall match of H/W & S/W is so good on the Z10 that you never need to look at your hardware specs or run task killers or system monitors. I don't even remember the clock speed/cores/RAM on my Z10. But I can rattle off those for any android device i have. Not so much a problem with iOS though.
There is no issue of "No SD Card" "Non Removable Battery" either in Z10 (though Z30 does have a non removable battery). So overall this is one phone where I don't miss anything which would usually push me to try some other device.
Off course, with BB now going down, i will need to shift to some other device in a year or two. Depends on how long Z10 lasts. To be frank it won't last as long as an iphone i admit. Apple devices do have exceptional longevity and really good resale values even after a few years.
Anyway, that my 2c. Your views may differ. I am just trying to tell you it WAS a great product which is going down. But all features will probably be picked up by iOS and Android or any new entrant (dare I say Ubuntu Phone). Already the youtube and facebook apps for android have a few nice swipe left/right gestures which are good and useful.