For the most part, Windows Phone 7 has had great reviews. Below lies the fundamental difference between how Apple looks at things and how the rest of the industry does. Google and Microsoft often adopt new features in their products because they are "cool" and that the fact that you can do them is clever. Apple has not worked to integrate social media into their OS(instead allowing others to do so through their own third party apps) because the reality is that a synced Address Book with Facebook friends, Gmail contacts, etc don't always work well together. The different sources think of the term "friend" in many different ways.
What makes it worse, though, is when an OS tries to implement it. In example, read below (from Engadget's Windows Phone 7 review):
Windows Phone 7 doesn’t have “contacts,” per se — it has a People hub, and there’s quite a difference. This is a thoroughly social platform, and it doesn’t really seek to make any sort of differentiation between people you talk to / text / email, those you just casually observe, and those with whom you’re “friends” in name only. For typical email accounts — Gmail, Hotmail, Exchange — you’re given the option to sync calendars, contacts, email, and in some cases, photos. That’s perfect — the way you want it to work — but it isn’t consistent throughout the phone. For example, once your Facebook account gets added, everything gets added to the phone. And when a contact of yours uploads a photo, that image appears in your photo hub whether you like it or not. That means, for example, that your Pictures app could have a bunch of shots of your ex’s aunt’s new boyfriend’s dog in it (more on that in a bit), and there’s not a whole lot you can do to stop that behavior without completely removing your Facebook account from the phone. With Exchange or Gmail, this strategy is probably fine in most cases — contact sync is one of the main reasons you use Exchange ActiveSync. But seriously, Facebook is another matter altogether.
Just imagine, if inside my address book, where I scroll through to find a person to text or call, there was all of the people I follow on twitter and the 2,000 something friends on Facebook, their activity and everything in the way of me remembering their phone number.
Something tells me that a separate app for each function is far less annoying than scrolling through meaningless info you don't care about just to accomplish a simple task.
UPDATE: Another Example:
The first thing you notice when you open the Marketplace is that aside from apps, you’ve got music and games as available categories, whereas iOS breaks music and applications out into separate stores, and Android leaves music to third-party providers like Amazon. Swiping to the left takes you to the Featured page of the Marketplace, which oddly mixes up both music and applications into a single view — kind of an interesting way to keep people looking at everything Microsoft has to sell without trying to send users’ attentions to two (or more) completely unrelated places. Unfortunately, that same mixture happens for searches in the marketplace too, meaning that you’ll get mostly song and album info when you’re looking for something like The Harvest. Microsoft needs to give users a way to sort apps from music, because search is completely unwieldy as it stands right now.