Ranked in these QuestionsQuestion Ranking
Pro Large toolset
UDK has an extremely large toolset that allows creating almost anything without having to use a 3rd party tool or plugin.
Pro Triple A track record
UDK is an engine used by many big name companies for popular games such as the Gears of War series.
Con Superseded by Unreal Engine 4
Con Limits games to FPS
UDK was originally developed for the FPS, "Unreal Tournament", and it certainly shows. While UDK is a very powerful engine, it takes quite a bit of work to make it do something other than an FPS.
Con DevKit only runs on Windows
Even though UDK can deploy games to run on multiple platforms, including Mac, it does not feature support for development on Mac.