Ventajas
I found the people to very competent and kind, but the workforce is older and there is less social interaction than I have found elsewhere. Pay and benefits are good and the near term looks good ($100+ barrels of oil sure help keep profits over $10B a quarter). The opportunities to work international are available albeit in some less desirable places; far eastern Russia or Nigeria being two examples. The small perks of the job were nice -- great meals when the company took employees out, car service, good hotels, etc etc -- all the things that make business travel more enjoyable.
Desventajas
The workforce is older and thus younger employees might less people to mix with on a casual basis. Additionally, Exxon is very traditional company in terms of structure and management style. Very clear organizational chart lines let you know where you stand. Promotions seem to be based less on employee formally expressing an interest or applying to internal positions and more about the senior leadership deciding when you are ready and where you should go -- whether you initiate or desire that move is not a high priority. Finally, those that want to enter upper management will probably have a rotation at a refinery which is not the most desirable place to spend two years.