Ventajas
Google's management allows, or rather, encourages engineers to take as much ownership as they like of projects. Product managers are there to work with engineers to direct the product, as their job is to know the customers and the marketplace and come up with a good direction for products. Because a lot of what the marketplace wants is illogical, engineers often argue with product management, and such behavior is part of what makes engineering a great place to be. You can actually have a significant impact on product direction. Additionally, Google is very fair about how promotions work. The engineers who impress their colleagues get promoted. Those who don't impress their colleagues don't get promoted. Thus, most good engineers will get promoted. I've heard lots of people complain about this process, but usually I hear this from engineers who aren't that impressive. It could be that the explanation for *why* they aren't getting promoted isn't transparent enough...but I don't know. In almost all situations, you are in control of your own destiny at Google. You set your own goals. You set your own timeline to achieve those goals. Management is there to guide you in setting these goals, but it is your duty to set good goals and strive to achieve them. This is also very empowering, and avoids the micromanagement that occurs at other companies. Then there's the obvious, which everyone else has already mentioned, like the *great* food, the massages, the really understanding/flexible management when it comes to personal issues, the good benefit package, etc.
Desventajas
Google is big, so your impact often seems tiny with regard to the company as a whole. Things are gradually getting more and more bureaucratic, the pain of being a public company with profits to protect. You gradually feel less and less important to the company as time goes on, as the company grows to many 10s of thousands of employees. Things like the Founder's Awards, which originally were supposed to be motivating factors to great products could end up being demotivating for many. For example, if you are stuck on a project that is in maintenance mode, or if you launch a great product that is overlooked, you might have little motivation to work hard again.