Pros
For lack of a better way to say it, Google is just a fun place to work. There are a lot of different personalities and the attitude of the whole place is very relaxed. The best thing, however, is that this doesn't detract from the drive that individual employees and the company's leadership have to create great products and really make life better for millions (or billions) of people. It's refreshing to go to work every day with people who are very smart but still pretty down-to-earth. Another key benefit is the fact that the company is very open in terms of sharing information with its employees. Top-secret projects are regularly shared company-wide and help employees feel that they're really engaged with the company's mission and accomplishments. Finally, for product managers specifically, the scope of the job at Google is much broader than what you might get with a similar level of experience at other large tech companies, which makes you feel like you're making much more of an impact.
Cons
Despite Google's efforts to maintain a startup-like atmosphere, it's still true that big-company hurdles -- like legal issues, regulatory concerns, and just standard VP approval processes for big decisions -- can slow down the process of doing cool things. And although the average talent level is quite high, the discipline and effectiveness of individual engineers can still vary somewhat significantly, so sometimes you'll have to deal with people who just don't work as quickly or independently as you'd like. Finally, in an engineering-centric company like Google, a PM can occasionally feel a little like the "e-mailer in chief," a person who nags other people a lot but doesn't get to do "real" work and who doesn't get the same respect as an engineer.