Low poly is fine. In fact that's the best practice you can get. Similar to limited color palettes for sprites, it teaches style, restraint, and working with limitations.
Even in today's high poly games, artists need to strive to be as low poly as possible for what they're representing. The lower poly count, the more objects you can have rendered in a frame.
Look at some high end PSP games like Dracula X Chronicles, Megaman Powered Up, Maverick Hunter X, and Final Fantasy Dissidia. Their models are incredibly low poly for their looks. Texture mapping plays a huge role in how well the model looks, giving details and shaping techniques that you don't need to waste polygons for.