A startup company I worked for was bought by IBM. Some of things that I noticed:
Right after the acquisition you feel like superstars: I mean your shares are now worth real money and you are the shiny new thing in a large organization, but this is also because the number of steps between you and the CEO is pretty low, because the people who did the acquisition are pretty high up, and you probably now work directly for them. But over time, this distance grows as you fall in the hierarchy..
It is way better for your career to be an acquihire than a hire- you would start at higher band for sure.
IBM was different from Google in that there was no mono-culture (like a giant repo for all code). Instead other groups tried to get you to use their products. For example, we used perforce but boy did they try to get us to use
ClearCase and then Rational Team Concert. Of course our group would have to pay "blue dollars" to use those tools (vs. green dollars for Perforce licenses).
At least some parts of IBM are driven by trade shows. There is a need to show the latest new product at these shows, which drives internal invention and development. My experience was that few of these succeeded in the marketplace.
IBM, being such an old company had a much more normal distribution of people at it. There was much more age, race and sex diversity than at startup companies. There were many more mid-career people who were in the middle of raising their families, not just trying to change the world.
I'm sure this is the same as in Google: "thought leaders" advanced fast. Actual coding would not advance you- fixing bugs and adding planned features does not change the world.