I've had my Nexus 6 for 3 days now but I'm definitely missing my WP.
I know 3 days isnt long enough for a fair shake but oh well. I have a year or so probably to see if it grows on me.
-apps seem to crash more often than even 8.1 which was a step back for WP experience in that regard already.
--Chrome doesn't show the text I type in on web pages half the time. Its especially bad on forums.
-I dont like the way the back button works on android. As in I go back through that app, not what I was actually doing. So if I'm on the web and I get a text, respond and press back I see the list of texts receive instead of going back to web browsing
-Menus galore. Options everywhere and spread out everywhere
-On the notifications menu if I receive one email I can see the subject of it. But if I receive two it just says two messages received. Thats kind of annoying.
-WP home screen. I miss you
-keyboard is meh
-I can't find an easy way to block numbers from calling. I had to create a contact called blocked and add numbers to it and select that contact to send them straight to voicemail
+performance is awesome. Smooth (except crashes) no matter how much I have open.
+dat screen
+battery life is awesome. I'm still running off my charge from the night before last
+flexibility is awesome. I've been playing ff8!
+the speakers are incredible
Maybe I am just having withdrawals
Don't use Chrome. You're on Android, you have a gazillion alternatives like Firefox, Javelin, Dolphin or Opera.
On Android you can expand notifications. If you get two emails and it says just that, then swipe the notification down and you should get all subjects. If you have one and you swipe down, you get actions like delete on the lock screen. Super awesome.
With keyboards it's the same as with browsers. You don't have to use the default keyboard. Don't like it? Try SwiftKey, for example. It takes a bit until it gets your habits, so try it for few days, but then it can be pretty awesome. Gave it a try and still don't like it? Try an alternative. If you don't like the way it looks, you can pick a different skin as well. Some are free, some are paid.
The back button behavior is just a thing you're used to and it's actually a legacy behavior on Windows Phone, from the pre-Mango era, where it didn't have a multitasking view. On Android, try the app switcher. Again, it's something you have to get used to as well, but it makes sense and it's not as cumbersome to use as on Windows Phone or iOS.