The HOG plan (or ones similar to it) are very good for making the jump from "train set" to "Model Railroad".
A big problem with the 4x8 is that its space constraints tend to limit your options to 'round and 'round plans. Similar to the one you drew, actually. While these look good, and are fun to build (hey, what layout isn't fun to build?) they soon become quite boring, as all you can really do is watch the train go 'round and 'round. If that's all you want from your model trains, then maybe that's the way to go.
Most people find they become quickly bored with that sort of layout, though. It's good for a short diversion, but after you've watched the train do a couple of laps, you've added a couple more trees, you add a couple of ducks to the pond, you're wandering off to see what's on the tube.
The nice thing about a plan like the HOG is that you can run 'round and 'round if you like, but there's room for some switching, and lots of variety in scenery.
While the over-under thing looks cool (and it is), buildiing a layout just to get an over-under is a sure ticket to disappointment. Apart from the real-estate it takes up, it also provides all sorts of opportunities for frustration once the "under" track is hidden by scenery. Better to have your first layout wide open and exposed - fewer things to worry about and easier to get at your mistakes.