Unity is very close to being a wonderful piece of software. However, my experience with it has been very painful. Over the past month, I have been writing a voxel terrain system. Unity made this extremely easy to pull off, and I could get good results very fast. However, soon my problems began to set in. Over the course of about 2 weeks, around 15 different bugs occurred in the Unity engine, building up to a major show-stopping bug which caused Unity to crash repeatedly. So basically, there are way too many big bugs for Unity to be of any real use. It's very very close to being great, and I'm sure if you don't have any problems,then it is fantastic. But unfortunately, I was not that fortunate.