It was what I started with and I ended up liking it, so when I started working on Himeko Sutori professionally, I paid for the professional version and kept using it. That was the quickest way for me to make the transition uninterrupted. I’m not sure I can recommend it now though.
It was nice to be able to create UnrealScript projects from inside Visual Studio. And then it had a lot of options that you could set (they would be in the properties window in the image above, if it were working) for how you could play and test the game when you click debug. (I think under the hood it was just adding command line arguments.) And in addition to that, it had all the usual IDE stuff that you would expect–code completion and stuff like that.
Maybe I should look into Sublime if I’m going to make a pure UnrealScript project.