As others have said, IBM is so big that it can only really be understood as many different companies, all with slightly different cultures. There are plenty of people who are better qualified than me to discuss the overall strategy and financial picture, so I won't even try.
I can, however, give a few opinions about my 2+ years in GBS.
* There is a general lack of respect for technical skills. I was hired as a "Technical Consultant" but put through the same training as the business consultant grads, which is largely about project management / presentation skills. A lot of money is spent on this training, if you ask for funding to (e.g.) attend a developer conference, you are told to forget about it. Maintaining dev skills or learning new ones is to be done in your own time or as part of "giveback", which is the IBM name for extra work done on top of your day job.
* The leadership team is utterly obsessed with maximising billable hours. While this is understandable for a services business, it is taken to ridiculous extremes. People are under such pressure to be billable that they are forced into roles that are completely unsuitable for them, rather than spend a few days waiting for the right role. Training etc gets cancelled at short notice if billable targets are not met, especially in Q4. Last year the entire GBS UK workforce were banned from taking any vacation for several weeks in November and December. A spoof email from senior management was circulated, saying "Christmas is cancelled" which gives an idea of current morale.
* The annual appraisal (PBC) system is a popularity contest. The best way to game the system is to do "giveback" (see above) work for senior people and persuade them to write nice things about you. This is all well and good, but it means that performance in your main job role is actually secondary to how much eminence you can gain by doing odd jobs for senior management. Thankfully IBM has seen the light and retired the PBC process, so I'm looking forward to seeing how well the replacement works.
* I get the feeling that nobody really understands Watson. It seems like the senior execs are under a lot of pressure to buy into the hype and sell Watson to their clients. There is a lot of hand waving about using Watson in "virtual assistant" type of use cases, but I've seen very little of any substance.
* The bureaucracy can be incredibly painful. I once had to go through multiple layers of sign-off involving people in 2 different countries over several weeks, to buy a $25 software licence (which I needed urgently for my job).
* Things are changing, slowly. The iX service line is adopting a startup-like approach on some projects. Agile is being promoted in a big way, and we now have access to modern tools like Slack and Enterprise GitHub.
I hope I don't come across as a bitter, entitled millennial. These are just my opinions.