You need a procedural engine and a terrain creator so the game doesn't have a flat world. The days of hand-crafted terrains in a 3D game has been over for almost 30 years. In additon you need an automated asset dropper (using said PROCED engine) to reduce the amount of production time you are using while placing assets 'free-hand'. Most gaming companies have these (secondary pieces of software), but they are almost always made in-house. I have to assume UnrealEd is not going to provide these for you, or you would already be using them :) 99% of large 3D games made in the last 30 years were made using in-house software (secondary to the IDE and compiler). Lastly, the PCO needs as lil more grav.