Looking good! It's a nice, clean style that should be easy to produce assets for. The two main suggestions I have are to watch the gradients (in particular, the one on the car sort of clashes with the curved outlines) and to be bolder with your use of colors. Right now, it looks like you just use a darker and lighter version of the same hue for shading, but I think mixing that up would add a lot of energy to your work. Vary your hues more; shadows should usually be cooler and less saturated than highlights, and they should typically gravitate towards a common global shadow color, e.g. a dark purple or blue. You can also do the same with highlights if you ever do more complex shading.
Your simple, flat-shaded style kind of reminds me of Syosa's:
His use of color is excellent, and you should consider studying it.
Here is an interview with him where he talks about his style and how he picks colors. This diagram in particular illustrates what I mean about unified colors:
As far as the gradients go, I would consider experimenting with minimal use of shadow colors (again, Syosa's work is a good reference) instead of gradients. It usually looks cleaner with simple, bold pixel styles, although it does take more time, so that's a tradeoff you have to consider. Another thing that would add a lot is doing some anti-aliasing around your dark outlines to make them look smoother, but again, that takes time. The first image of Syosa's there is a good example of what I mean, though.
slym comes to mind as an artist whose environments you could draw inspiration from, although his backgrounds are maybe a little more complex than what you want:
Look at the wood and the bricks in particular. The shading is very minimalistic but implies texture.