UI customizationDunno - I enjoy the native UI, so I've never tried to customize it.
Maps I use Nokia Drive, also. Sorry, can't help ya.
MusicI've got Win8 on my home PC and once I showed XBox Music where all my MP3s are, it made most of them available to me through their cloud service.
I can now stream roughly 75% of my music collection to any Win8 device I own, for free.
Perhaps not quite as good as the way Google Music handles your music collection, because my music is only streamable from the cloud if it was already there - and some of my tracks aren't in the XBM cloud, but it's still a pretty nice feature.
Cloud Storage I use Skydrive, and have 28GB of free storage there.
Alarm clockI don't use my phone as an alarm clock, so I can't speak to this.
Honestly, I don't do a whole lot with my WP.
I've got my Facebook, Google, and work calendars all in one.
I text/FB chat through the messaging app. Love how it handles that.
I use Nokia Drive and Nokia Music (I'm still on a WP 7.5, so I don't have XBM on my phone) but neither very frequently.
My single favorite app would probably be SoundHound, for those "omg, what song is that?" moments.
Primarily, I treat my phone as my "need to look something up on the internet
right now" device.
Thing is, and this has been said before, which smartphone you use sort of comes down to either:
- One or more specific apps you must have, that can only be had on one platform
- Which cloud service you're most tied to
If you're already pretty much tied to the Google cloud, and have no pressing need to switch, I honestly wouldn't recommend doing so.
I didn't already have an iPhone or Android when I got my Windows Phone, so I wasn't tied to anybody's cloud yet.
Now I'm kinda tied to the Microsoft cloud and can't easily imagine what it might take to convince me to switch.