Android Q is the code name for the version of Android that Google will release in 2019. At some point in the future we will learn what "Q" represents, in the past Google has associated releases of Android to deserts.
Here I will track information about this version of Android. I have not yet installed this version of Android on my Pixel 2, I don't normally install it until it is near ready for release. Update: installed Beta 6 on 8/14/2019, see below.
Google's Android beta program site 
Probably the easiest-to-notice change in Android Q is the slicing up of settings for each individual app. Android Q brings about “Settings Panels” that pop up from the bottom of each app, where applicable, showing system settings in the context of each app. Slashgear
The second beta release introduced multi-tasking bubbles. page
Beta 4 is now here and it brings with it a ton of updates, improvements and overall feature enhancements to really whet the appetite ahead of the next release. 9to5Google
We’re just a few weeks away from the official release of Android Q! As we put the final polish on the new platform, today we’re rolling out Beta 6, the last Beta update. page
Android Police has a comprehensive overview of all the changes in Android Q. page
Google has announced that hence forth there not be any more desert names associated with Android releases. The next release will only be known as Android 10. page
Android 10 final was released to Pixel phones on September 3, 2019. page
My Personal Experience
I've enrolled my Pixel 2 in to the beta, let's see what I get. A few hours later I received the notification on the Pixel 2 that the update was available to download and install, which I installed later in the evening with no problem.
I have to confess that I don't know all of the features of Android Q, most the the changes appears to be either cosmetic or under the hood. Two that I know of, dark mode and navigation gestures I enabled if for nothing more to see something different.
I don't normally like dark mode. For example, reading white text on a large back background messes with my eyes. However, I do find dark mode on the smaller screen to be appealing. I think that might have to do with the fact that the white text isn't really as bright or I just don't look at the screen long enough.
I find that I like the new navigation gestures, to me they enhance one-hand operation of the phone. I do wish there was a middle screen, top-down gesture to display the system drop-down menu as my thumb cannot reach the top of the screen while hold the phone in one hand. When I hold the phone in one hand the bottom right corner sites in the palm of my right hand.
I've walked thru all of the features of Android Q as presented by 9to5Google .
I've learned about a gesture that activates Google Assistant. Start a diagonal swipe from the lower right or left corner and hold until you hear a beep and the Assistant dialog displays. Speak when you hear the beep. Android Police
The notification to download and install the final release of Android 10 appeared on my Pixel 2 late afternoon on September 3, 2019. I directly downloaded and installed. page