The facial expressions on the plant are very emotive. Very good. However, I'm a little concerned about the mouths on the people. I'm not sure that you'll be able to have enough definition there to get the different between a smirk and a smile. With the woman in white, the mouth is too close to the chin area, which has a lot of dark pixels, making it very difficult to make out the expression (if you are going 2x pixels, this probably won't be as much a problem).
The black outline and light shading will make a huge difference when you try to place these characters against a bunch of different backgrounds. What works against a dark busy background doesn't always work against a light solid color, so you really need to show these characters off against several different backgrounds to make sure they work. The definition of the plant's stem could be lost in a busy dark background, for instance, so you might want to use lighter colors there to make it pop out more. Only way to know is try.
Pixel art comics... what will they think of next...?