I've been Windows mobile user for about couple of months, and as you stated, I'm a hardcore user.
I first had a BB 8820 and I really liked it, after that I bought a HTC Fuze and I have to admit it, it was awesome, in past because I sold it 3 days ago.
a) One point to Winmobile is its customizable environment: I had like 2 o 3 UI installed on My device: TouchFLO 3D, SPB Mobile etc..
The major point on winmobile is the functionality: one could use dial up on a Windows phone and even tether another phone to use its data capabilities, its just like a computer.
The back-draw of Windows Mobile is the fame of Microsoft among Hardcore users:
A lot of people think that just because it says "Microsoft" is something unworthy or useless with a lot of issues, because the bad experiences they had have on a PC. It's just not right.
b) I see Windows mobile as a hidden treasure, that few people knows its true capabilities.
It's a fact that WM6 and previous was targeted to Stylus users, but HTC has made a big improvement with TouchFlo adding a layer of finger control on the Surface of the devices.
c) Windows will keep the functionality and improve the UI on the devices, I'd like to see more ties with the Live platform, I know there are more things that they can conquer within their products.
d) The Blackberry Users will like the almost PC environment, could play almost any video file, the ability to access the registry for a quick tweak, even having dual boot for more than one Operating System on the device.
Note here: On my Fuze I had Windows Mobile 6.1, later 6.5, Android 1.6, later 2.1 and I saw Blackberry Application Suite on the a HTC FUZE for an almost full Blackberry OS function on it, very handy.
One thing the BB users will lose is the push mail for several accounts, actually the only free Push service on Wmobile is the Hotmail, and only one account. Hotmail push emails as they arrive. Exchange may help, but you need to get it via third party offers.
e) The app situation is not like 'There's an app for that' but one could get useful things out there.
The browsing on WM is smooth, can even play small Flash animation actually, My device came with Internet Explorer 6 and Pocket IE, I could choose both for browsing.
There's also Opera and Skyfire, which provides a complete browsing with Flash and Silverlight support for WMobile devices.
The games are so so, I had quite a few games, on new devices one could play OpenGL 2.0 games and hardware accelerated.
For mention: Xtraxt, Experiment 13 are 3D based games that look like Wow, is this for real??
For quantity there are tons of Cabs spread over the Internet and in the Marketplace too.
For quality I would say it's useful enough.
I had been 3 days without my phone and I feel kind of lost without my appointments, tasks, full browsing and tweaking my device.
I'm looking forward for Windows Mobile 7, that I hope it will be better than now
