Have had mine for a couple of days, and I like it quite a bit. Call is getting tougher as to which device I pick as my dedicated phone 4S or Lumia 900. The 900 is not an iPhone killer, but it is a killer alternative if you've got an upgrade due and 30 days to try it.
My review below is SOLEY based on user experience, and phone functionality. NOT app counts which we already know the score on, and isn't fair to judge a relatively new (I only count post Mango update) OS. Should wp ever reach a healthy six digit app count, the race may look a lot different.
It really is a cool OS, and if people brought an open mind to it, they might actually like wp or at least break even on what they think about it.
At any rate....
Love being able to pin a photo album of my 7-mo-old daughter on the home screen!!!!
UI is cool and different, more fun to "play" with
Ease of interacting with people seems to be a lot faster
You can get to more functionality in fewer steps
Tiles make it easier to get to info
Nokia design is pretty cool
Bigger screen is nice, Clear Black Super AmOLED is really nice. No, not retina awesome (so stop before you make comparisons), but still holds it own. Better than the Titan and Focus S for sure.
4G is pretty fast
Battery is pretty good
Got the APN update today and the phone works great now, looking forward to my $100 AT&T credit.
I like the email client better
Keyboard with word suggestions works better for me
Music player is pretty good
Nice to try apps before buying
WPCentral forums are really helpful for converts
You can put media on the phone purchased in iTunes, that's really nice!
Skydrive for free
Only 16gb's, if this was 32gb, they'd sell really well
Notifications take a little more time to track down
No expandable memory
Didn't come with headphones (although I've got cyan Monster iSport headphones that match!!)
APN issue was a bummer, but only for 36 hours, so not bad.
I would like to have seen the 900 the size of the 800. Played with one night and liked it a lot because of the form factor.
Doesn't seem to be cloud backup like iOS.
Contacts are a pain when setting up the phone. I got a ton of duplicates. WP is a lot smoother from this standpoint.
So, as you can tell, it's a good device. And I'm a pretty happy Apple customer since I bought my Project Red 2nd/4thGen Nanos and green 5th gen. Includes 3G, 3GS, 4 and 4S phones as well as 1st/3rd gen iPads, 3rd gen iPod touch and iPod video.
All of that apple history and I still like the 900!