I don't think those are examples of great software. They are very useful, and many fill a niche that needed filled, but they aren't great software IMO. Hadoop is a very leaky abstraction to give one example. I've seen it crash frequently because people used wild cards for their input and the job tracker would run out of heap and crash.
Hadoop is a leaky abstraction because it crashes ? Does not compute!
I'm not very familiar with the others, but Lucene is really an example of great software. In a few lines, it makes you feel as if you can build a Google by yourself !
