Looks interesting but why not use Unity?
Depends on what you want to use it for. UDK has a very awesome system called kismet in it that is a very powerful system that kind of reminds me of a spreadsheet but is meant to "code" your games. It's essentially an "eventing system" for the Unreal engine.
The biggest problem I have seen is the community is very hush hush on their work and aren't too friendly when it comes to helping people figure out things. Most questions regarding things like "how do I make melee weapons" or whatever is met with technical talk that the original poster of the thread doesn't know much about and "learn unrealscript" replies. I haven't found many reliable UDK/Unrealscript tutorials outside of the basic tutorials offered on the UDN knowledgebase and even that seems to be rather lacking. If I could just find a book or something that covered the basics, I would be a happy man.
The picture in my art thread with the gate to hell was a little art project of mine done in the UDK. If you are more of a designer, the UDK is really easy to get involved with compared to unity.
I also would like to point out the licensing SEEMS more flexible for the UDK if you were to decide to make an indie game and sell it.
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