When I started my N scale Old Line Corridor experiment last year, one of my objectives was to be able to run trains--whole trains, MUd locomotives, maybe even have meets and passes on the layout. In short, I wanted the OLC to be like railfanning somewhere on or near the Northeast Corridor, where big railroading happens.
Across the basement over at the HO scale Dunes Junction, there are trains running, to be sure, but the experience is decidedly unlike railfanning a former Pennsy (or any) mainline. It's more like a visit to a South Shore or Northwest Indiana railroad museum, where lovingly restored vintage rolling stock does 'over-and-back' moves around a section of restored right-of-way.
It's mostly the small size of N scale that is allowing me to see and experience the trains similarly to how I see and feel them in reality. Rarely do I actually see individual rolling stock up close, as at a museum; I'm more likely to see a locomotive or two trailed by freight or passenger cars that extend beyond immediate my field of view, passing through the landscape of suburban Maryland where I live or in the places I visit.
Realistic and controlled movement play an equally important role. The overall high quality of contemporary N scale locomotives is key to this measured movement of implied momentum and mass, but DCC deserves significant credit as well. The fidelity of control offered by DCC--particularly enhancement of lower speed control but also the ability to program lower top speeds--means that trains move more like the prototype. I've never experienced better or more versatile control of my trains.
Not sure I have ever experienced this sensation of realistic, massive movement on a layout of my own, and if I have experienced it with HO trains it was at a club or museum layout, such as when I visited the San Diego museum layout a few years ago. But I am surprised and delighted to see big ol' trains on my modestly-sized home layout.