Pros
The best thing about Blizzard were that people that actually created. I spent most of my time interacting with different game development teams and QA. For the most part the low and mid level personnel were extremely passionate and dedicated to making a quality product. Allowed QA to set a very high standard (at least when related to bugs and crashes).
Cons
I saw the downhill slide occur first hand during development of Starcraft II. People in a leadership role on that project and battle.net slowly eroded all of the good will Blizzard had built up over 15 years of previous battle.net functionality. Removing LAN plan, removing chat rooms, facebook integration - these are all things that no game anywhere wanted. The pushback internal on this was monstrous, yet it was wholly ignored. The results speak for themselves. Battle.net is an afterthought and SC2 is just another game that some people occasionally play. This behavior of making decisions contrary to the best interests of the gamer/customer for short term profits also bled into the Development of Diablo 3. The auction house was lauded internally as a complete disaster, yet higher ups pushed ahead and the disastrous results are all too clear. Some change has been made (2 years later) to close it down, but the damage done is obvious. In the late 90's and early 2000's the only games I played were Blizzard games. Warcraft 2, Starcraft, Diablo 2, Warcraft 3. I haven't played a Blizzard game regularly since 2010. The Blizzard that most of us knew, admired, and wanted to be a part of is long gone. If you work for the company now, you will work long hours with great people for substandard pay on products that you won't play. Work at your own risk.