Once you open up an issue, flipping through pages is a snap. You can swipe left and right one by one, or tap to pull up page thumbnails for faster flipping. There's also a table of contents on the bottom-left, though it's mostly text based, which isn't quite as fun as the thumbnails. If the text on a page gets too small to read, the pinch-and-zoom gesture helps. Otherwise, you can switch to a fully text-based version of any page, which kills most of the visuals, but gives you the option to change text size to enhance readability.
For the most part, tablets and phones offer similar viewing experiences (except for the screen size, of course). A vertical screen shows you a single page at a time, while a horizontal orientation gives you a full-page spread.
When it comes to performance, Google Play Magazines could use some work. Even though issues were saved locally on my devices, I routinely experienced some lag when loading, with some pages taking a few seconds to show up. Some users have complained that pages failed to load altogether, but I didn't experience the issue in my tests.
Overall, if you're into magazines and you love doing your reading on your mobile devices, Google Play Magazines is a fantastic choice. Since Android users are already fairly locked into the ecosystem, buying subscriptions and individual issues through the Google Play service should be a snap. We hope some of the performance issues are addressed in the next version of the app.