Managua is a noisy dive. I did not feel safe. A special type of gringo would enjoy this sprawling low rise city. There are many areas where walking is not recommended. When I give it a second thought, this may be the ugliest state capitol I have ever seen. It is one of the very few cities where I never want to go back unless I have to.
Nicaragua is a very poor country. I went with my nursing school to help family's out. This little girls touched my heart. If you every get the chance try to make a trip there. It's a very beautiful country with volcanoes and wonderful beaches!
I lived in Managua for a summer while in grad school and recognize that it is a point of arrival and departure for most people, rather than a destination. That said, you may find yourself needing to spend a few days and nights there and it is not the worst thing in the world. The city is diffuse, and the devastation of the earthquake in the 70s is still apparent. So, if you are looking for a place to stay where you can also go out and do some things, you want to stay in Zona Rosa or Zona Hippos. These areas are almost contiguous, and further away from the "center" of town and the Malicon along the lake. They are near the Carretera Masaya, contain most of the modern business district as well, and they are generally safer than some of the places downtown where the Lonely Planet leads backpackers. The Hotel Princess is a Hilton hotel in Zona Hippos, and there are some nice, smaller places as well. Managua won't be the highlight of your trip, but it does not have to be a nightmare either.
It's extremely busy, and there is a lot of crime.