If you want some examples of what even an amateur can accomplish with these sets, I'd recommend checking out the
WorldWorks Games User galleries. There's *lots* of great stuff on there.
This stuff has a fairly low learning threshold. Definitely far easier than, say, learning to paint minis. But don't exactly expect your first attempt to be representative of what you can achieve with just a little more practice...
Probably the single biggest thing you can do to make your models look better is to "edge" the pieces - i.e. run a marker along the white edges of the cardboard. That alone can make the difference between "crappy cardboard model" and "oh wow!". Other than that, it's mainly an issue of learning to switch your blades frequently, and how much glue to use so you get a strong bond without warping. With a little practice, it's fairly easy to get something that'll look great on the table.
As far as "professionally built models", most of the promotional images (all of which are also on the
WWGallery) aren't really "professional quality" builds - at least not comparable with people spending weeks to paint a single 25 mm mini, or months to build and paint a professional quality Hirst Arts diorama. Denny's models for example (i.e. most of their fantasy line) are printed on a embarrasingly low-budget Lexmark inkjet printer, and put together in a hurry in the rush to put the product out. I wouldn't be surprised if Denny spent far more time doing the lighting and photography, and putting those beautiful flash movies together, than actually *building* the damn sets.
