Unity is an intuitive game development engine that offers a vast array of features for both 2D and 3D game development. It is one of the best engines for cross-platform mobile game development. You can quickly and easily port games onto Android, iOS, Windows Phone 8, and BlackBerry platforms. Unity supports assets from major 3D applications like 3ds Max, Maya, Softimage, CINEMA 4D, Blender etc. With the recent release of Unity 4.3, native 2D capabilities, supporting sprites and 2D physics are also added to its design capabilities.
Though Unity integrates with all major 3D applications, there are many limitations to its editing capabilities inside the engine editor. Apart from some primitive shapes, everything has to be created using a third-party 3D application. Alternatively, you can always purchase assets from the asset library(pricing is determined by the asset author). Also, with the new 64-bit support and WebGL, Unity 5 is evidently a strong contender among the mobile game development engines.
The Unity engine comes with many pricing options. The Pro version of Unity, which is $1,500 or $75/monthly per seat and per platform. There is also a Unity 5 Personal Edition which includes many common features like Profiler, Physically-based shading, Reflection Probes etc. However, there are many qualifying criteria to get that license. For more details, you can visit the Unity pricing page.