I was overjoyed on March 20, when I heard that Unreal Engine 4 was released and not only that; but it would only cost $20. a month. I purchased it soon after and have been having a lot of fun with it.
There is no doubt that Unreal Engine 4 is a powerful game engine. What is especially nice is that there are many tutorials on how to use it already and the documentation is complete enough to have all sorts of things to try. There are even complete games with source code that you can use and modify.
The main downside for me is the lack of available content to use for prototyping. UDK is still the winner their and Unity as well. I will post new information about Unreal Engine 4 soon.