I've had a total of 3 HO layouts so far over the years - 2 were 4x6, one was a 4x8. I enjoyed each, but others might be frustrated by the limitations. Suggestions for enjoying small layouts in HO (conversely, if you can't stand these ideas, reasons you won't be happy with a small layout in HO)
- short trains. A train 30" long (short engine and 4 40ft cars) is about the longest practical train able to do more than watch it chase it's tail. It's also about the longest practical passing track you can fit on a 4x6 ft layout. You can run one longer train on those occasions when you just want to watch a train run.
- short locomotives. Why waste train length on a large locomotive? Small locos will llook much better with your short trains and on the sharp curves. Small locos will easily handle the number of cars you can put in a train.
- use short cars. Again, the shorter the cars, the more you can put in your train. Anything longer than 50ft (7 inches) is going to look out of place on the curves. Use shorty passenger cars (60ft and smaller).
- model an appropriate era and prototype. To me, trying to model modern day Class I railroading with 100 car trains being hauled at 60 mph by giant diesels on a 4x6 is an exercise in frustration and a waste of good modeling $$. The older you go, the smaller locomotives, cars, and trains were. There is one exception - the early diesels (1940s and early 1950s) were often smaller and less powerful than their modern steam (1910 onward) counterparts. Car length held pretty steady from about 1910 to the early '50s. Picking a specific era and/or prototype to model helps limit the "buy some of everything" at the hobby shop, and helps prevent having too many cars and locomotives for a small layout. Selection for eras older than 1940 becomes more limited but with a little searching every era can be modeled without building from scratch in HO.
- keep your roster small. Reality is that 2 decent running locos are all you need. A dozen freight cars and 3 passenger cars are about all that will fit reasonably. Anything more ends up being stored off the layout. The small roster lets you spend time building and modifying kits, further reducing your $$/hour for the hobby. You can also concentrate on making those few cars and locos really nice ones.
- build at least one dramatic scene such as a tunnel entrance, a dock, an overpass, a trestle, or something similar. The idea is to be able to watch your train run through a scene you particularly enjoy, one you'll want to take pictures of and share.
- consider using a mix of sectional and flex track. It is not easy to get consistent 15" and 18" radius curves with flex track, so I recommend using sectional track in those areas. But replacing the smaller "fitter" track pieces and straight track with flex will make your track smoother, fewer joints, and flow better. Also switches (turnouts) are not sacred, they can be shortened. You can cut the portions beyond the frog (where the rails cross) or before the points without harming the turnout. By shortening the turnouts where needed, you can make many more track arrangements practical.
- if you are going to run more than one train at a time, consider using DCC for control. Keeping block toggles sorted for 2 train operation on a small layout takes the fun out of running a train. On the other hand, if you are only going to run one train at a time (except maybe on rare occasions) avoid the extra expense of DCC and the hassle of installing decoders in your locos.
- design a layout with switching opportunities. Since multi-train timetable ops are going to be quite limited, providing freight car switching is the feasible alternative to watching the train chase its table.
- consider an expansion off an end or side. Some real fun-to-operate small layouts come from adding a town or yard as a 2x6ft (or 1x5 or 2x8) extensions to a table layout.
- if you have the room, expand to 4x8 or even 5x8. Makes a huge difference in the track plan options. Using foam construction will keep it light enough to be moved easily. Build in 2 sections for the ultimate in portability.
Some 4x6 track plans I really like:
- Morgan Valley. At Atlas web site. Track will not fit as shown, need to use flex in place of small curves and straights. Excellent switching opportunities.
- Tidewater Central. Dec 1956 Model Railroader project. Needs a couple of spurs added to improve switching opportunities. Great scenery possibilities. One of the ones I built
- East Haven and Wharf. Early '60s in Model Railroader. Good switching with a wharf for interchange.
- original Gorre and Daphited. In 101 Track Plans. Although 4x7, it offers a twice-around, over-and-under with limited switching opportunities.
- Simplicity and Great Plains. At Atlas web site. Needs to have spurs rearranged so they don't all face same direction.
Hope this helps