With the introduction of the NEM wheel standard the standard wheels now look a bit better, but you can do even better by changing the wheel sets on your rolling stock with the more prototype-like RP25 wheel sets. This is done without messing with the running characteristics of your rolling stock.
Some people will argue that the model even runs better with the RP25 wheel sets, but that is not my experience, so you should only do this if you want to add an extra layer of detail to your rolling stock. You will have the same running characteristics as you always have.
RP25 is Recommended Practice no. 25 of the NMRA
I bought my replacement wheel sets from modellbahn-radsatz.de they have replacement wheel sets for almost any manufacturer, the ordering process is quick and easy and you can pay with your credit card. The price is just right as well and a lot cheaper than other manufacturers (e.g. a genuine Roco RP25 wheelset is 2.9€ at MB-R.de it’s 0.85€! Way cheaper than Roco’s overpriced stuff). When ordering you can choose whether you want isolation on both sides or just the one side. I would recommend one side isolation if you are to pickup power from the tracks on passenger cars.
Take a look at some of my pictures and judge for yourself. I surdenly like it and I think you should give it a try. There is no harm done to the model, you can always change the wheel sets back should you not like it. Replacement wheel sets are usually 2-rail only, if you run 3-rail (aka. Märklin) I would not recommend you try this.
For the record, the couplers are temporary.