Pros
Beautiful campus and great benefits (Health Care, vacation, sick time). If you push yourself to interact with everything that is offered (talks, clubs, cultural events, and even affiliations with JPL!) you can learn a great deal and have fun outside of work. In the right department, you can be treated well with room to grow. There are amazing people working here in all areas. Associate with the right ones and you will learn and expand your horizons. Get stuck in the wrong group isolating yourself and you'll stagnate and be unhappy.
Cons
Caltech is losing the independent thought and expression that made it great. Corporate thinking is encroaching and there's a strong "do more with less" attitude. Staffing numbers are dwindling in many departments and budgets are shrinking.