Well matey I have the Lumia 1520 - so the bigger brother of the Icon.
Windows phone has come a long way and the experience is always consistent and hassle free - much like iOS.
The negatives are mostly at the lack of some of the most common iOS / Android apps that many of us use without thinking, but the situation is certainly no where near as bad as it was just a couple years ago.
Nokia really do have a great build quality, and phone reception / call quality is very good on my 1520. Indeed call quality is better than any of my previous phones from last year.
There are quirks to the OS GUI that are frustrating. The settings menu needs to be categorised and tabbed, because it often feels randomly laid out. Takes longer to find your brightness controls than it really should for example.
App folders which are only a recent addition are also not very well implemented, and need much more refinement.
Text messaging and the keyboard on windows phones is great for me - the auto correct is as good as the best android and the best on iOS.
Voice control is poor enough at the moment, but with the forthcoming 8.1 update it looks set to sort that out with Cortana.
Notification centre would be handy and is coming. A way to put all your notifications in one place especially when you have a notification from an app that you don't necessarily want to have pinned to your desktop home screen.
Battery life on my 1520 has been genuinely unbelievable. I can get through a day of normal usage with only 25-35% gone and thats with 3 email accounts / twitter / Facebook / snapping some photos / editing photos / reading emails / sending texts and making phone calls / reading news feeds.
Standby drainage likewise is exceptional in my experience.
If the Lumia ICON has it (and I bleive it does) - the tap to wake is great (as you know from your HTC M8) and the Nokia applications are of a very good quality.
Nokia MixRadio is my main music app - I much prefer it to Microsoft's MUSIC & VIDEO app. Indeed the whole suite of Nokia apps are excellent including Nokia maps and Nokia Drive.
Bluetooth and Nokia Drive are great, with the phone having no issues pairing to my car and having hassle free bluetooth experience.
Sound quality through headphones has been fantastic - and the device supports Dolby Digital for the headphones and it shows. The sound quality is subtle but also noticeably better than it was on my Note 3.
Windows Phone software on Mac is actually not bad - especially given HTC Connect and Samsung Kies ....
Gmail accounts sync without issue with the stock email and your calendar and contacts likewise all sync without issues - however you may indeed miss things like Google Play Music especially if you are a subscriber.
My legacy .mac email addresses all sync fine - but Calendar and Contacts didn't. However as I migrated those over to gmail a good while ago this didn't pose a problem for me.
Negatives are that customisation is limited compared to what we are used to - but hopefully 8.1 brings more customisation to the table. I would love to either put a background image on my tiles or even behind them. I'd like an easier way to choose whether I want a tile to be a live tile or not. Font resiszing can be fussy with changes to font size in settings effecting only parts of the OS and not all of it. Internet explorer for the most part works ok, but it does at times have issues with text font sizing too.
Sometimes third party apps - used to fill the hole of missing apps like YouTube just don't feel as good often. MetroTube as good as it is - just isn't as good as the stock YouTube app on iOS & Android.
I'm not sure I could live with just a windows phone - but it could and has been a daily driver for me and for the 90% of tasks we do on a smartphone - it does them very well and with no delay (other than its GUI animations/transitions).
I'm excited to see what refinements and additions 8.1 brings to the table.
