UDK is Unreal Engine 3 – the complete professional development framework. All the tools you need to create great games, advanced visualizations and detailed 3D simulations. The best tools in the industry are in your hands.
I use UDK at University I've Recentley created a small kismet example map for my course, it's a fun and creative program, featuring some cool little utilities such as the good old brush with additive and subtractive geometry,and the awesome kismet and matinee animation so simple and easy to construct, Fill out your map with lovely textures, imported into UDK and applied by creating materials which allow endless tweaking!!!, I am yet to unravel the mistery of Unreal Script, but thats just me VS coding and such,
LEVEL DESIGNERS AND GAME CREATORS >>> UDK <<<< xD
I've found UDK to be flexible, in the sense that you could easily make almost any sort of game for it with any sort of camera type, with some trial and error and tutorial help or past knowledge ofcourse.
It's also being updated monthly, sometimes with just fixes and minor feature updates, but sometimes like recently larger updates like adding a debugger to Kismet.
I have found UnrealScript to be a nice language to work with, if somewhat strange at times, I've also recently taken my first steps into developing Kismet related code and it seems Kismet is a really powerful tool for giving power to a level designer, requiring much less effort from the programmer to open up that power.
Overall, it's just a great engine and toolkit, updated monthly without being forced to update and with the right progamming knowledge at least you prototype a game much faster than anything I've ever worked with.
This engine is wicked sick, it may have a steep learning curve even with tons of user-made tutorials, yet. The flexibility it haves makes it the best option in the market to start a new entry into the world of video game developing.