Windows Phone is both the best and the worst mobile platform available right now. I believe its user interface is by far the best looking and most useful of the three main platforms out there. It is available on hardware ranging from the sublime (the Lumia 1020's class-defining camera) to the ridiculous (the Lumia 435, the smartphone for the price of a t-shirt) and it works very well on the full spectrum of hardware.
The app gap remains though, despite all of Microsoft's efforts. It's amazing how many third-party developers have stepped up to fill the gap left by the original developers, but there are still too many gaps. The biggest absence is Google. Google doesn't make its apps available for Windows Phone, a gap which often cited by reviewers as an insurmountable barrier to adoption.
First of all Gmail/Calendar, Maps, Translate, Google Now, Docs and Snapseed all have direct Microsoft equivalents which are as good or better than the Google clients. Unless you are dogmatically tied to the Google service (in which case just get an Android phone) they shouldn't cause you problems when switching.
To the apps which matter then. The first of which is YouTube, perhaps the most contentious of the missing apps. Microsoft, in a move which was either provocative or borne of frustration, built its own YouTube app which was at least as good, if not better than Google's offerings on other platforms. Google wasn't happy and forced Microsoft to remove it. Fortunately there are several alternatives in the Windows Phone Store, my current personal favourite being Tubecast, which supports everything the official YouTube apps on Android and iOS support including streaming to Smart TVs and Chromecast. About the only thing you can't do is upload video. Fortunately Upload to YouTube is available in the app store, which integrates with the phone's sharing interface to allow you to upload your video from within any app.
There is no official Google+ client, although there are several third party apps in the Windows Phone Store. In this case there's not really a need for an app, as G+ has a capable mobile website which offers all of the functionality, if not quite as slickly as the official mobile apps. If you need an app then Google+ View wraps up the mobile site into a pleasant package.
Blogger's client on iOS/Android is pretty grim, lacking in features and control over the posting process. Personally I don't use it on either my iPhone or Xperia. I find that posting using Blogger's email service works just as well. If you have to use an app there are a few in the Store. Pin Blogger looks nice and works well, just be aware that like all WP8 Blogger clients image uploading isn't currently supported.
Google Drive also has a mobile website, but to be honest if you're thinking of switching to Windows Phone you'd probably be better off moving your online storage to OneDrive. If you must use Drive then Google Drive on WP does the essentials. Similarly if you're a user of Play Music, switching to Spotify or Xbox Music gets you all of the same functionality and, in the case of the latter, is both cheaper and includes 100GB of additional OneDrive storage.
For Hangouts and Voice, Skype offers a more than capable alternative. There are also some obscure Google properties like Ingress and Field Trip that occupy a small niche and some hardware specific software like Glass and Wear that are tied to Google's devices. Otherwise I think pretty much everything else is covered.
So if you're a user of Google's services and you're thinking of switching, it is possible, with a few compromises. The app gap remains but it is possible to bridge it.