I started to do programming tutorials in UDK. its scripting is not bad. if you do anything, it is always built heavily on existing classes, so first you have to know them well, but finally it also provides you a lot of ready to use features. it is likely not for one person development at all, becaue it is time consuming to explore all of its secret parts...

so if you get from Esenthel what you need, it is easier to use, and good quality is also possible relatively easily. (this is where 3dgs falls a bit behind, it can be programmed well, but to get a really up-to-date appearance, you have to write your own set of shaders from the basics.) some months ago Esenthel offered some source access in the store, but as I see it is removed. earlier you got some source access to game classes if you bought a licence, now it is not mentioned. its licensing is changind quite dynamically