I was there for 2 weeks staying with my brother in law. Within a few hours drive you could be either in the middle of downtown Nairobi (chaos) or so far out in the sticks there was only a faint path to follow for miles around.
If you avoid the man-made slums the scenery is very nice but it's the wildlife that is more compelling. Zebra, antelope, wildebeest, giraffes in abundance. What was amazing to me is that you could drive for a couple hours on a dirt path, and out of nowhere there would be a small Masai village. And there would be a small store, and that store would have Coke and Fanta for sale. Where the heck does it come from?
The roads are horrendous and even in the city you have to be prepared for a 12" deep pothole, or the edge of the road to suddenly narrow by a couple feet, at any time. Out of the city the paved roads are not quite wide enough for two cars to pass at high speed comfortably, so you have to pay attention to oncoming traffic in case they want too much out of the middle of the road.
The people were very nice and when I was with them I spent most of my time answering questions about the US.
My favorite story was sitting around a fire at night with the askaris, talking about the US, when I had to sneeze. I pulled out my handkerchief and sneezed a couple times, then blew my nose into it, folded it up and put it back in my pocket. There was a minute of silence before one of the askaris said, "Excuse me, Mr. kranky, may I ask you why you are saving that?"