It's Black Level performance (primarily) and the ability to reveal dark shadow detail that essentially separate great projector picture quality from ok, or good picture quality.
Take this Pro Cinema 4030 for example. One could compare it to Epson's own, less expensive Home Cinema 3020. The hardware and features are very different, but I'm talking image.
On bright and medium bright scenes, both of these projectors - with their similar brightness, will look very close to each other. Oh, the 4030 will have darker blacks on those scenes, but you likely wouldn't notice unless you really were comparing side by side.
On the other hand, switch to a really dark scene and there is a real difference: As we all know dark scenes are very, very, common. Try to find a movie without some - good luck!
Basically, the Epson 3020 is just dandy, with little image difference compared to the 4030 on average and well lit scenes, but not those dark ones.
The 3020 can look, compared to the Pro Cinema 4030, very washed out on a scene like the Bond night train scene we show in every review. Dramatic difference. That folks is why you spend the extra net of $400 or $500 for the Pro Cinema 4030. If you don't care, or your room is never darkened, the difference is mitigated, but otherwise, that Bond train scene, the 5th Element Starship scene, and the Hunger Games sleeping in the woods scene, as they say, are the money shots!
Mind you, move up to the more expensive Pro Cinema 6030 UB, and it's even better at blacks, but the difference is a lot less than going down to the 3020!
Time to take a close look, let's start with Black Level Performance.