Maybe UnrealScript was just too damn complex. Having not used it, and just Googled it, my first reaction was "this looks just like C++ anyway". What's language features are there specificity catered for games? It doesn't seem very DSLy
It had synchronous-style code for handling animation logic, without needing hundreds of threads.
It also had some clever ideas about replicating state across the network. You want to run the simulation locally to reduce latency, but you also need it to run elsewhere to have a consistent source of truth. So some state would be calculated by the local simulation, but be updated when packets of truth arrive. Member variables could be annotated according to how they were replicated, IIRC.
Time and State are first class constructs in UnrealScript, they are not in C++.
It's also possible to recompile UnrealScript files without recompiling the whole C++ program which took quite a while. (Unreal4 allows hot reloading C++ so this is no longer an issue.)
There were a few constructs for dealing with scripts running on the client vs server and also data replication across the network built into the language. This is where it different from being just a scripting language.
Ultimately it was confusing at first. Besides the official docs I had to look at their script source and old UT2 tutorials to figure it out.
I haven't seen the new engine, but I imagine simply doing a net.replicate(&player_info) would have been more straight forward than dealing with all of the unrealscript language constructs for it.
