I'm not sure how far you can expect to go with a touch pad... there is a reason why painters have been using brushes and pens and the like for ages. But anyway, here's my recommendations, coming from someone who can't really draw anyway but likes to shoot off his mouth...
Firstly, you write that you spent about ten minutes on each of these. Frankly, with tools like what you're using you can't expect to create a great masterpiece in ten minutes. It's just not going to work. If you want fast, look into getting a graphics tablet. Even the low-end wacom tablets are pretty good (as long as it says "wacom" somewhere on the case, it should be fine). I figure that learning hand-eye coordination anew is not going to be a problem if you're already using a touch pad anyway, which has the same issue. And when you get one, expect to spend more than ten minutes on a painting too. You write yourself that you were too fast with the background in the landscape painting. I can't add much to that observation. If you want detailed, spend time on details. They don't come out of nowhere unless you really really know how to use a brush.
Secondly, your two portraits look like you used a photograph as a reference. I suggest that before you try copying photographs, you should get a book on the subject and study the basics. There is a tonne of material out there that is intended to teach people how to draw and not be "utterly rubbish at doing it" (your words). In particular, there are ways to construct a face so it looks real, that is, where to place the important bits that go in a face and all that. Again, be prepared to spend a little more than just a few minutes on anything you do. Over time you will learn how to draw with less and less construction, but as long as you haven't learnt that, it's extra time you need to spend on each piece.
Thirdly, none of your paintings have any sort of shading. Even with a sketch, just a little shading can make a huge difference. Again, there are books out there that cover this and you should try and get hold of one and read it. To illustrate this, I'm attaching a very basic sketch of a head, with little to no features detailed. See the difference between the first and the second column? Both are coloured in one flat colour, but the second column has some limited pencil shading applied. The fifth version additionally has added shading with a darker skin tone. I'm not very good at this myself, but even then, see what kind of a difference you can get from thinking about the spatial layout of your scene and your light sources for a few minutes? Again, it's important to know why the colours are different in different areas, don't just try to imitate something you see in a photograph. A photograph will completely remove some details that you need to see if you want to learn this on your own. With a real person, you can move your light sources, or look at them from different angles, you can't do that with a photograph. Fortunately, everything that you would learn from doing this is explained in those books that I keep mentioning, so you should get one already. As a bonus, they typically contain much better explanatory imagery than what I can provide ;-)
Finally, in addition to spending more time and thinking more about your layout, you should practice your technique as well. Fortunately, those same books that I keep talking about also teach you that. With that said, I will shut up about books now and I hope you didn't read this as more harsh than it is meant to be read as :-) Just keep practicing, and enjoy what you're doing, and eventually you'll learn to fix the bits that you don't like yet!