1. It syncs with Zune Desktop Software, which is like Microsoft's iTunes. It's a multimedia player/device manager, it's fast, beautiful and really enjoyable for playing music. You can set it to sync whatever you like and required to update your phone.
2. There's kindle for Windows Phone, it works great. Cut The Rope is missing, but yesterday EA announced a partnership with Nokia that will bring all chillingo games to WP very soon + EA exclusive titles. Google+ is not in the marketplace at the moment. :I guess you can't have it all, but I don't find it personally NECESSARY. spotify is coming soon, Whatsapp was realeased about a month ago, there's angry birds, PvsZ and many other games.
3.In one year life, the OS has been updated thrice, first update with some performance improvements, second with copypaste, third update was Mango which brought a ton of enhancements/features to the OS (around 500 new features). the next major update is set to come mid 2012 with two smaller updates previous to that.
4.Gmail syncs beatifully in Windows phone (all email providers do, in fact) Google calendar syncs automatically in the calendar app when you sync your email account (and works great), there isn't much about google docs, just the web app. But it has full sync with Office360 and the Office hub in the phone is just marvelous (seriously).
5. Outlook is also deeply integrated with windows phone, although I'm not sure about that exact question, as I'm not an outlook user myself.
6. Well, with the mango update, my phone (Omnia 7) can go about two full days with no charging at all, before the update it only lasted less than a day, and Microsoft says improvements are bound to happen.
7. Windows Phone is a phone for people that want something to JUST WORK. it doesn't ask you very specific questions on irrelevant things, it doesn't give you advanced settings to every single thing or lets you do things like rooting/flashing etc... It's a practical phone. You power it, put your Live ID, facebook and twitter and there you go, it's running. it comes with many features already built-in so even though some apps are lacking, it hardly ever feels the phone is lacking something. Bing replaces out of the box shopsavvy, google search, shazaam, maps. People takes out the need of a twitter app, facebook, linkedin, and foursquare. messaging has facebook chat and WLM integrated in threaded conversations. The camera can go from pocket to facebook in seconds (with tagging and face recognition integrated)
My advice would be to consider what you are: a power user (that needs lots of customization, nitpicking etc...) or you're a practical user (that wants something that works and helps you do what you want to do).
The biggest + to windows phone I say it's the people hub. It really helps you stay in touch with those you care about and see what they're up to in the moment.