AT-op Recently came from android too, been an android user for several years and mostly got Samsung Flagships.
I used the following smartphones - symbian ( 6600, 6630, n82 ) - maemo N900 then jumped to android SII, Note II , Note III.
I can tell you the OS is fluid as it gets, without flashing custom roms, launchers and loosing your warranty ( samsung knox ).
I'll agree with you that the keyboard is not the best possible and the lack of alternative keyboards/launchers is annoying,
but that was something i was aware of before i got my Lumia.
They keyboard could be a lot better for me if they just added number support with long pressing the top row!! ( very simple, can't understand why not implemented yet ).
IE could be a lot better, always used firefox in my droid. However have high hopes for the new browser in WP10.
Although the market does not have the large number of apps, available in iOS and droid, most of not all the useful apps are there.
The only app i used in droid and its not available in WP is K9-mail client, however the integrated mail client is almost as good.
That said, if you scroll the droid apps, you will find that more than half are a piece of **it, why would i ever use 100+ flash light apps ? 100+ fart apps, screen crack apps, make weird noises apps etc ?
You may also miss some games, but im not "phone gamer" thats why i have my pc, casual games for when on bus/train etc are available, although i really miss quizup.
Other pros i can think of are :
-build quality
-UI
-camera, although i use my dslr when traveling having the lumia camera for quick snaps is a joy.
-don't have to reboot the phone every ~1 day, so i doesn't lag.
-have had my L1520 for ~2months, had no random restarts.
-I don't have to install 3rd party hardware to limit mobile traffic and back round activity of apps. Can be done through the integrated apps/os settings.
-WP support for old devices is priceless, updates go out a lot faster and don't depend on the phone manufacturer to release the OS update for my 1 year old flagship, which they intentionally delay so they can sell the new models.
I don't think nokia should go android, since they ditched maemo-meego (which were the best mobile OS i've ever used ) they should stick with it.
The market apps will only get better/more support as the user-base increases. A thing MS is trying to achieve by having there apps released in other OSes.