Vantaggi
I had a great time working with the former Sun Microsystems part that Oracle Corporation acquired in 2008. Specifically working on the Solaris kernel. This part I like--a lot. I worked with one of the best teams of people in terms of talent and being part of a cooperative, fun team. Pay is good--or at least competitive. Being a big company gives many opportunities to look around elsewhere if you don't like what you are doing now. The top-management are competitive and have business smarts (if not always technical smarts).
Svantaggi
Huge bureaucratic company with many processes to slow productive work down. The corporate level seems hostile to cutting-edge technology and research. Too many layoffs--they seem to perfer to layoff than reassign people. My part of the company, former Sun Microsystems/Solaris/SPARC, is now gutted and doesn't really exist any longer except for a skeleton crew for sustaining support.