Very well done! This has got an eerie loneliness to it. It is simple, but there could be a lot going on. They look to be in the middle of nowhere, which makes the viewer think that there is no one else around, but they are also stopped, either for the portrait or for something else. Perhaps something caught their eye. Maybe it's just the blinder by the horse's eye which prevents us to see where it's looking, but the horse seems to be gazing off at that tiny shadow on the horizon. Is there some significance there, or am I thinking too much?
Overall, this is exceptional work. This piece is aching for a storyline to go with it, but the fact that it's a painting leaves us no choice but to guess at what might be going on, or just to use far too much imagination and read into subtleties that are nowhere but in our mind.