I actually still use WP7.5 (though 7.6 has also been released) for the simple reason that it was cheaper than Apple and not Google (call me paranoid if you will but I have problems putting some of my trust into Android). And this was a really nice alternative.
Looking back Microsoft really should have kept their promises and tried to appeal much more to the developer / geek market instead of trying to milk it dry. I mean... E 100,- payment for the right to mess with your own phone (developer unlock)? Also (for context): for a platform which had yet to proof itself. Who in their right mind would do that? Sure, this ridiculousness was soon dropped, but by that time it also really was too little and too late.
I really think it could have worked, when done right. Obviously the horror which was Windows 8 also didn't really help. When I told people how I thought that Metro wasn't all that bad I quickly attracted weird looks, do you really think those would buy into Windows Phone once they learned it ran Metro, that which many fully despised on Windows 8?
Oh well, I suppose we still have Blackberry. Oh wait, we don't because those have also been fully converted to Android.