Pros
MTG has a great work environment... the location, my co-workers and the challenge of my job make for fast days and not dreading going to work each day. Management values my opinions and contributions, and they don't hesitate to tell me. I've been at too many jobs that only focus on what an employee is doing wrong, which is depressing and makes you want to look for something new. Mercury breeds loyalty by putting their employees at the top of the food chain and has no qualms about showing their appreciation of a job well done.
Speaking of food... we have a full kitchen, complete with an oven, microwave and refrigerators so making some good leftovers for lunch is easy and fast. Plus, they have a dedicated kitchen and office assistant that brings in fresh fruit everyday and makes lunch runs for the entire office.
Overall, my experience at Mercury has been an enjoyable one. It's always great to be able to come up with new technology and have fun while you're at it.
Cons
I really haven't come across anything that annoys me here. Mercury has been on their game with proactively conquering any issues before they become REAL issues, so it's been smooth sailing since I started.