Vantaggi
IBM is only great if you're just about to start your career. Once you've learnt everything and have something to show on your CV, move to another company where you are actually appeciated.
Svantaggi
There is not enough time in the world to list all cons. IBM is a great place of fake talent. Everybody is faking, especially those people who have "expert" in their job title. Management is exploiting employees to the fullest, if somebody leaves the team, they don't hire someone new but you will need to do the leaver's job too as a default from then on. Appreciation in return? None. Even if you would be willing to work overtime, it's not paid, or if it is, it's just simply not worth the effort. There is a process for everything and that would make you think everything is working smoothly but quite the opposite: IBM is chaotic, bureaucratic and trying to live off of its old reputation. Well guess what: it doesn't live up to its name at all and it's simply a miracle that it still hasn't sunk yet.