Hopefully I can answer your question.
I just came from Android as my last 3 smartphones.
I was a Google ******. Lived by Gmail and all their other apps and programs. Gmail still is my person email, even with the move. For work, it's all Microsoft, so I decided to transition due to all the Android hardware eventually giving me trouble (and I only keep phones for 8-16 months).
Anyways, with WP8, I use the built in mail client. Sign into Google and it'll sync your contacts with all their information, and obviously your email. You'll get all your folders/labels as well. It's smooth and no problem. Also, when you add a new contact, you can have the option of adding it to Google.
MetroMail is great as well. I downloaded it and use it occasionally. It gives you a more Google feel, but on a Windows Phone skin. You can't go wrong with either.
If you are just sending/receiving tons of emails, the built it would suffice. However, take a look at MetroMail.
No, you don't have the Google based apps on the phone, but 3rd party apps work great (Google Maps, Google Voice, etc.).
I see no difference in my Gmail while on Windows Phone. I've had no issues.