Pros
IBM has an incredible amount of projects going on simultaneously which gives prospective employees many different teams that they can apply to. Some require special PhD degrees, other programming jobs hardly require college. The teams work well together and if you're a programmer that's what you'll be doing. They have dedicated translation teams, documentation teams, translation teams, etc that take care of work that isn't really your job.They make it very easy to transfer projects/teams within IBM and it's encouraged which is great for building your skill set. Hours are relatively flexible and managers have a hands-off approach which lets people mind their own business as long as they produce great results.
Kontras
Projects can be very boring and feature work can seem extremely useless. Young innovative engineers don't drive IBM's products, rather, corporate executives with little to no programming experience decide what should get done. This leads to a culture where programmers are facepalming, in disbelief how stupid some work will be, while trying to fulfill the management's requests. Developers are very very low on the management chain, so you'll have tons and tons and tons of managers above you preventing employees from raising any real issues, concerns, or advice. The entire development buildings are filled with cubiciles so there is little to NO employee interaction. I only had lunch with teammates on the last day I was there, meanwhile I knew 30 of the interns. The culture is just boring and dry and it's reflected in the projects they tend to create. The company is incredibly frugal, skimping on everything from toilet paper to overpriced food you need to pay big for. They'll count and charge you a lot for every strip of bacon you think about eating. Your first week will have 0 productivity as the company's autorization servers are numerous, slow, etc, and the software they force you to use is absolutely horrible. They made their own email client and its the slowest, most bloated POS I've ever used, which is similar to most of the software they make.