I'm attempting to build such a language (you can find a link in my profile if you're interested. I don't want too much attention yet since I'm planning on a first release later in the year). You're right it can become difficult to follow code when it's not presented in a linear fashion. The flip side though is that you can write code in smaller chunks that can do a lot, so you write far fewer lines overall. The other thing is that it opens the door to more advanced tooling than we're used to as developers: things like time travel debugging, saving program state and querying it, or running hypothetical execution paths to find the best one. Bret Victor is famous for demoing prototypes of these debugging tools in one of his talks, and they are finally becoming real.

My language turns out to be very fun to write UIs and games in, so I'm glad you honed in on those two examples. Actually one way to view it is that it's a programming language with a game engine as a runtime. But robotics is the primary application I'm targeting.

In fact I had to choose between lazy and eager evaluation, and I've chosen eager because I want latency guarantees. With a lazy evaluation scheme, I was unsatisfied with the windup that would occur in some situations that would totally blow performance. And we don't have to recalculate everything all the time; we only have to recalculate the paths that have an input change. This may lead to recalculating everything, but most of the time we only have to focus on the execution path that is "dirtied" by the updated input.

Anyway if you want to test drive such a language as you're imagining, send me an email and I'll give you a tour/demo. The language isn't really user-friendly yet so there are some pointy edges that make it unusable to new users at this time (which is the main reason I don't want more attention on it until that is resolved.)