So they've chosen to use Unity to power Wasteland 2. Their announcement actually has a sort of defensive air about it - http://www.kickstarter.com/projects/inxile/wasteland-2/posts/228226 - like they're expecting people to complain. Me, I think Unity is the obvious choice - if I was on the project it would be my first choice too.
But for a somewhat ineffable reason: happy workers are more productive. Working with Unity is such a pleasure it makes me happy just to use it. I get to code in C#, for one thing. And if I want to know how to do something I don't know how to do, usually a quick google search such as "Unity environment maps" gets me the answer I'm looking for and bam! I can make it happen. And it's not lacking in power - I've done tests where I've had hundreds of flocking AI's running at 60.