For me, the most killer feature of Qt Creator is that it its humble resource needs and lightning quick response. It never leaves me waiting for anything. It has consistently felt responsive and stable as long as I have been using it (5 years) .
Another important feature that Qt Creator has is that it's native and cross platform. This means that it does not need any bloaty VM to be installed such as .NET framework, Java VM or similar. When you install Qt Creator it is a statically linked C++ application built natively for your platform.
Qt Creator is tightly linked to the Qt framework and has many features built in to support Qt such as graphical UI designers, UI resource manager, 3D asset management, Internationalization manager, debugger integration with support for Qt native types. It also has a test harness built in and support forthe Qt spesific build systems (qmake and qbs). Review collected by and hosted on G2.com.