Well it's a bitmap programme, just like Paint or Photoshop. Therefore anything you can make in those you can make in GIMP. It's more a question of format, you can't make vectors or 3D stuff, but anything you can physically see on a screen you can replicate. Vectors and 3D art are still represented on the screen via pixels so you could make that, but only one static image, and it won't be scalable.